diff --git a/src/Aspire.Cli/Npm/NpmProvenanceChecker.cs b/src/Aspire.Cli/Npm/NpmProvenanceChecker.cs
deleted file mode 100644
index 423b5e1e686..00000000000
--- a/src/Aspire.Cli/Npm/NpmProvenanceChecker.cs
+++ /dev/null
@@ -1,233 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Text.Json;
-using System.Text.Json.Nodes;
-using Microsoft.Extensions.Logging;
-
-namespace Aspire.Cli.Npm;
-
-/// <summary>
-/// Verifies npm package provenance by fetching and parsing SLSA attestations from the npm registry API.
-/// </summary>
-internal sealed class NpmProvenanceChecker(HttpClient httpClient, ILogger<NpmProvenanceChecker> logger) : INpmProvenanceChecker
-{
-    internal const string NpmRegistryAttestationsBaseUrl = "https://registry.npmjs.org/-/npm/v1/attestations";
-    internal const string SlsaProvenancePredicateType = "https://slsa.dev/provenance/v1";
-
-    /// <inheritdoc />
-    public async Task<ProvenanceVerificationResult> VerifyProvenanceAsync(string packageName, string version, string expectedSourceRepository, string expectedWorkflowPath, string expectedBuildType, Func<WorkflowRefInfo, bool>? validateWorkflowRef, CancellationToken cancellationToken, string? sriIntegrity = null)
-    {
-        // Gate 1: Fetch attestations from the npm registry.
-        string json;
-        try
-        {
-            var encodedPackage = Uri.EscapeDataString(packageName);
-            var url = $"{NpmRegistryAttestationsBaseUrl}/{encodedPackage}@{version}";
-
-            logger.LogDebug("Fetching attestations from {Url}", url);
-            var response = await httpClient.GetAsync(url, cancellationToken).ConfigureAwait(false);
-
-            if (!response.IsSuccessStatusCode)
-            {
-                logger.LogDebug("Failed to fetch attestations: HTTP {StatusCode}", response.StatusCode);
-                return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationFetchFailed };
-            }
-
-            json = await response.Content.ReadAsStringAsync(cancellationToken).ConfigureAwait(false);
-        }
-        catch (HttpRequestException ex)
-        {
-            logger.LogDebug(ex, "Failed to fetch attestations for {Package}@{Version}", packageName, version);
-            return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationFetchFailed };
-        }
-
-        // Gate 2: Parse the attestation JSON and extract provenance data.
-        NpmProvenanceData provenance;
-        try
-        {
-            var parseResult = ParseProvenance(json);
-            if (parseResult is null)
-            {
-                return new ProvenanceVerificationResult { Outcome = parseResult?.Outcome ?? ProvenanceVerificationOutcome.SlsaProvenanceNotFound };
-            }
-
-            provenance = parseResult.Value.Provenance;
-            if (parseResult.Value.Outcome is not ProvenanceVerificationOutcome.Verified)
-            {
-                return new ProvenanceVerificationResult
-                {
-                    Outcome = parseResult.Value.Outcome,
-                    Provenance = provenance
-                };
-            }
-        }
-        catch (JsonException ex)
-        {
-            logger.LogDebug(ex, "Failed to parse attestation response for {Package}@{Version}", packageName, version);
-            return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed };
-        }
-
-        logger.LogDebug("SLSA provenance source repository: {SourceRepository}", provenance.SourceRepository);
-
-        // Gate 3: Verify the source repository matches.
-        if (!string.Equals(provenance.SourceRepository, expectedSourceRepository, StringComparison.OrdinalIgnoreCase))
-        {
-            logger.LogWarning(
-                "Provenance verification failed: expected source repository {Expected} but attestation says {Actual}",
-                expectedSourceRepository,
-                provenance.SourceRepository);
-
-            return new ProvenanceVerificationResult
-            {
-                Outcome = ProvenanceVerificationOutcome.SourceRepositoryMismatch,
-                Provenance = provenance
-            };
-        }
-
-        // Gate 4: Verify the workflow path matches.
-        if (!string.Equals(provenance.WorkflowPath, expectedWorkflowPath, StringComparison.Ordinal))
-        {
-            logger.LogWarning(
-                "Provenance verification failed: expected workflow path {Expected} but attestation says {Actual}",
-                expectedWorkflowPath,
-                provenance.WorkflowPath);
-
-            return new ProvenanceVerificationResult
-            {
-                Outcome = ProvenanceVerificationOutcome.WorkflowMismatch,
-                Provenance = provenance
-            };
-        }
-
-        // Gate 5: Verify the build type matches (confirms CI system and OIDC token issuer).
-        if (!string.Equals(provenance.BuildType, expectedBuildType, StringComparison.Ordinal))
-        {
-            logger.LogWarning(
-                "Provenance verification failed: expected build type {Expected} but attestation says {Actual}",
-                expectedBuildType,
-                provenance.BuildType);
-
-            return new ProvenanceVerificationResult
-            {
-                Outcome = ProvenanceVerificationOutcome.BuildTypeMismatch,
-                Provenance = provenance
-            };
-        }
-
-        // Gate 6: Verify the workflow ref using the caller-provided validation callback.
-        // Different packages use different tag formats (e.g., "v0.1.1", "0.1.1", "@scope/pkg@0.1.1"),
-        // so the caller decides what constitutes a valid ref.
-        if (validateWorkflowRef is not null)
-        {
-            if (!WorkflowRefInfo.TryParse(provenance.WorkflowRef, out var refInfo) || refInfo is null)
-            {
-                logger.LogWarning(
-                    "Provenance verification failed: could not parse workflow ref {WorkflowRef}",
-                    provenance.WorkflowRef);
-
-                return new ProvenanceVerificationResult
-                {
-                    Outcome = ProvenanceVerificationOutcome.WorkflowRefMismatch,
-                    Provenance = provenance
-                };
-            }
-
-            if (!validateWorkflowRef(refInfo))
-            {
-                logger.LogWarning(
-                    "Provenance verification failed: workflow ref {WorkflowRef} did not pass validation",
-                    provenance.WorkflowRef);
-
-                return new ProvenanceVerificationResult
-                {
-                    Outcome = ProvenanceVerificationOutcome.WorkflowRefMismatch,
-                    Provenance = provenance
-                };
-            }
-        }
-
-        return new ProvenanceVerificationResult
-        {
-            Outcome = ProvenanceVerificationOutcome.Verified,
-            Provenance = provenance
-        };
-    }
-
-    /// <summary>
-    /// Parses provenance data from the npm attestation API response.
-    /// </summary>
-    internal static (NpmProvenanceData Provenance, ProvenanceVerificationOutcome Outcome)? ParseProvenance(string attestationJson)
-    {
-        var doc = JsonNode.Parse(attestationJson);
-        var attestations = doc?["attestations"]?.AsArray();
-
-        if (attestations is null || attestations.Count == 0)
-        {
-            return (new NpmProvenanceData(), ProvenanceVerificationOutcome.SlsaProvenanceNotFound);
-        }
-
-        foreach (var attestation in attestations)
-        {
-            var predicateType = attestation?["predicateType"]?.GetValue<string>();
-            if (!string.Equals(predicateType, SlsaProvenancePredicateType, StringComparison.Ordinal))
-            {
-                continue;
-            }
-
-            // The SLSA provenance is in the DSSE envelope payload, base64-encoded.
-            var payload = attestation?["bundle"]?["dsseEnvelope"]?["payload"]?.GetValue<string>();
-            if (payload is null)
-            {
-                return (new NpmProvenanceData(), ProvenanceVerificationOutcome.PayloadDecodeFailed);
-            }
-
-            byte[] decodedBytes;
-            try
-            {
-                decodedBytes = Convert.FromBase64String(payload);
-            }
-            catch (FormatException)
-            {
-                return (new NpmProvenanceData(), ProvenanceVerificationOutcome.PayloadDecodeFailed);
-            }
-
-            var statement = JsonNode.Parse(decodedBytes);
-            var predicate = statement?["predicate"];
-            var buildDefinition = predicate?["buildDefinition"];
-            var workflow = buildDefinition
-                ?["externalParameters"]
-                ?["workflow"];
-
-            var repository = workflow?["repository"]?.GetValue<string>();
-            var workflowPath = workflow?["path"]?.GetValue<string>();
-            var workflowRef = workflow?["ref"]?.GetValue<string>();
-
-            var builderId = predicate
-                ?["runDetails"]
-                ?["builder"]
-                ?["id"]
-                ?.GetValue<string>();
-
-            var buildType = buildDefinition?["buildType"]?.GetValue<string>();
-
-            var provenance = new NpmProvenanceData
-            {
-                SourceRepository = repository,
-                WorkflowPath = workflowPath,
-                WorkflowRef = workflowRef,
-                BuilderId = builderId,
-                BuildType = buildType
-            };
-
-            if (repository is null)
-            {
-                return (provenance, ProvenanceVerificationOutcome.SourceRepositoryNotFound);
-            }
-
-            return (provenance, ProvenanceVerificationOutcome.Verified);
-        }
-
-        return (new NpmProvenanceData(), ProvenanceVerificationOutcome.SlsaProvenanceNotFound);
-    }
-}
diff --git a/src/Aspire.Cli/Npm/SigstoreNpmProvenanceChecker.cs b/src/Aspire.Cli/Npm/SigstoreNpmProvenanceChecker.cs
index 03f46bcb6cb..8cf739342ff 100644
--- a/src/Aspire.Cli/Npm/SigstoreNpmProvenanceChecker.cs
+++ b/src/Aspire.Cli/Npm/SigstoreNpmProvenanceChecker.cs
@@ -8,31 +8,10 @@
 
 namespace Aspire.Cli.Npm;
 
-/// <summary>
-/// The parsed result of an npm attestation response, containing both the Sigstore bundle
-/// and the provenance data extracted from the DSSE envelope in a single pass.
-/// </summary>
-internal sealed class NpmAttestationParseResult
-{
-    /// <summary>
-    /// Gets the outcome of the parse operation.
-    /// </summary>
-    public required ProvenanceVerificationOutcome Outcome { get; init; }
-
-    /// <summary>
-    /// Gets the raw Sigstore bundle JSON node for deserialization by the Sigstore library.
-    /// </summary>
-    public JsonNode? BundleNode { get; init; }
-
-    /// <summary>
-    /// Gets the provenance data extracted from the DSSE envelope payload.
-    /// </summary>
-    public NpmProvenanceData? Provenance { get; init; }
-}
-
 /// <summary>
 /// Verifies npm package provenance by cryptographically verifying Sigstore bundles
 /// from the npm registry attestations API using the Sigstore .NET library.
+/// Uses Fulcio certificate extensions and in-toto statement APIs for attestation analysis.
 /// </summary>
 internal sealed class SigstoreNpmProvenanceChecker(HttpClient httpClient, ILogger<SigstoreNpmProvenanceChecker> logger) : INpmProvenanceChecker
 {
@@ -56,22 +35,49 @@ public async Task<ProvenanceVerificationResult> VerifyProvenanceAsync(
             return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationFetchFailed };
         }
 
-        var attestation = ParseAttestation(json);
-        if (attestation.Outcome is not ProvenanceVerificationOutcome.Verified)
+        // Extract the SLSA provenance bundle JSON from the npm attestation response.
+        var bundleJson = ExtractSlsaBundleJson(json, out var parseFailed);
+        if (bundleJson is null)
         {
-            return new ProvenanceVerificationResult { Outcome = attestation.Outcome, Provenance = attestation.Provenance };
+            return new ProvenanceVerificationResult
+            {
+                Outcome = parseFailed
+                    ? ProvenanceVerificationOutcome.AttestationParseFailed
+                    : ProvenanceVerificationOutcome.SlsaProvenanceNotFound
+            };
         }
 
-        var sigstoreFailure = await VerifySigstoreBundleAsync(
-            attestation.BundleNode!, expectedSourceRepository, sriIntegrity,
+        SigstoreBundle bundle;
+        try
+        {
+            bundle = SigstoreBundle.Deserialize(bundleJson);
+        }
+        catch (Exception ex)
+        {
+            logger.LogDebug(ex, "Failed to deserialize Sigstore bundle for {Package}@{Version}", packageName, version);
+            return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed };
+        }
+
+        // Verify the bundle with a policy that uses CertificateIdentity.ForGitHubActions
+        // to check the SAN (Subject Alternative Name) and issuer in the Fulcio certificate.
+        // This verifies the signing identity originates from the expected GitHub repository.
+        var (sigstoreFailure, verificationResult) = await VerifySigstoreBundleAsync(
+            bundle, expectedSourceRepository, sriIntegrity,
             packageName, version, cancellationToken).ConfigureAwait(false);
         if (sigstoreFailure is not null)
         {
             return sigstoreFailure;
         }
 
+        // Extract provenance from the verified result's in-toto statement and certificate extensions.
+        var provenance = ExtractProvenanceFromResult(verificationResult!);
+        if (provenance is null)
+        {
+            return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed };
+        }
+
         return VerifyProvenanceFields(
-            attestation.Provenance!, expectedSourceRepository, expectedWorkflowPath,
+            provenance, expectedSourceRepository, expectedWorkflowPath,
             expectedBuildType, validateWorkflowRef);
     }
 
@@ -105,11 +111,16 @@ public async Task<ProvenanceVerificationResult> VerifyProvenanceAsync(
     }
 
     /// <summary>
-    /// Parses the npm attestation JSON in a single pass, extracting both the Sigstore bundle
-    /// node and the provenance data from the SLSA provenance attestation's DSSE envelope.
+    /// Extracts the Sigstore bundle JSON string for the SLSA provenance attestation
+    /// from the npm registry attestations API response.
+    /// Returns the bundle JSON on success, or <c>null</c> if the JSON is malformed or
+    /// no SLSA provenance attestation is found.
     /// </summary>
-    internal static NpmAttestationParseResult ParseAttestation(string attestationJson)
+    /// <param name="attestationJson">The raw JSON from the npm attestations API.</param>
+    /// <param name="parseFailed">Set to <c>true</c> when the input is not valid JSON; <c>false</c> otherwise.</param>
+    internal static string? ExtractSlsaBundleJson(string attestationJson, out bool parseFailed)
     {
+        parseFailed = false;
         JsonNode? doc;
         try
         {
@@ -117,134 +128,69 @@ internal static NpmAttestationParseResult ParseAttestation(string attestationJso
         }
         catch (JsonException)
         {
-            return new NpmAttestationParseResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed };
+            parseFailed = true;
+            return null;
         }
 
-        var attestations = doc?["attestations"]?.AsArray();
-        if (attestations is null || attestations.Count == 0)
+        var attestationsNode = doc?["attestations"];
+        if (attestationsNode is not JsonArray { Count: >0 } attestations)
         {
-            return new NpmAttestationParseResult { Outcome = ProvenanceVerificationOutcome.SlsaProvenanceNotFound };
+            return null;
         }
 
         foreach (var attestation in attestations)
         {
-            var predicateType = attestation?["predicateType"]?.GetValue<string>();
-            if (!string.Equals(predicateType, SlsaProvenancePredicateType, StringComparison.Ordinal))
+            if (attestation is not JsonObject attestationObj)
             {
                 continue;
             }
 
-            var bundleNode = attestation?["bundle"];
-            if (bundleNode is null)
-            {
-                return new NpmAttestationParseResult { Outcome = ProvenanceVerificationOutcome.SlsaProvenanceNotFound };
-            }
-
-            var payload = bundleNode["dsseEnvelope"]?["payload"]?.GetValue<string>();
-            if (payload is null)
+            var predicateTypeNode = attestationObj["predicateType"];
+            if (predicateTypeNode is not JsonValue predicateTypeValue)
             {
-                return new NpmAttestationParseResult
-                {
-                    Outcome = ProvenanceVerificationOutcome.PayloadDecodeFailed,
-                    BundleNode = bundleNode
-                };
+                continue;
             }
 
-            byte[] decodedBytes;
+            string? predicateType;
             try
             {
-                decodedBytes = Convert.FromBase64String(payload);
+                predicateType = predicateTypeValue.GetValue<string>();
             }
-            catch (FormatException)
+            catch (InvalidOperationException)
             {
-                return new NpmAttestationParseResult
-                {
-                    Outcome = ProvenanceVerificationOutcome.PayloadDecodeFailed,
-                    BundleNode = bundleNode
-                };
+                continue;
             }
 
-            var provenance = ParseProvenanceFromStatement(decodedBytes);
-            if (provenance is null)
+            if (!string.Equals(predicateType, SlsaProvenancePredicateType, StringComparison.Ordinal))
             {
-                return new NpmAttestationParseResult
-                {
-                    Outcome = ProvenanceVerificationOutcome.AttestationParseFailed,
-                    BundleNode = bundleNode
-                };
+                continue;
             }
 
-            var outcome = provenance.SourceRepository is null
-                ? ProvenanceVerificationOutcome.SourceRepositoryNotFound
-                : ProvenanceVerificationOutcome.Verified;
-
-            return new NpmAttestationParseResult
-            {
-                Outcome = outcome,
-                BundleNode = bundleNode,
-                Provenance = provenance
-            };
+            var bundleNode = attestationObj["bundle"];
+            return bundleNode?.ToJsonString();
         }
 
-        return new NpmAttestationParseResult { Outcome = ProvenanceVerificationOutcome.SlsaProvenanceNotFound };
-    }
-
-    /// <summary>
-    /// Extracts provenance fields from a decoded in-toto statement.
-    /// </summary>
-    internal static NpmProvenanceData? ParseProvenanceFromStatement(byte[] statementBytes)
-    {
-        try
-        {
-            var statement = JsonNode.Parse(statementBytes);
-            var predicate = statement?["predicate"];
-            var buildDefinition = predicate?["buildDefinition"];
-            var workflow = buildDefinition?["externalParameters"]?["workflow"];
-
-            return new NpmProvenanceData
-            {
-                SourceRepository = workflow?["repository"]?.GetValue<string>(),
-                WorkflowPath = workflow?["path"]?.GetValue<string>(),
-                WorkflowRef = workflow?["ref"]?.GetValue<string>(),
-                BuilderId = predicate?["runDetails"]?["builder"]?["id"]?.GetValue<string>(),
-                BuildType = buildDefinition?["buildType"]?.GetValue<string>()
-            };
-        }
-        catch (JsonException)
-        {
-            return null;
-        }
+        return null;
     }
 
     /// <summary>
     /// Cryptographically verifies the Sigstore bundle using the Sigstore library.
-    /// Checks the Fulcio certificate chain, Rekor transparency log inclusion, and OIDC identity.
+    /// Checks the Fulcio certificate chain, Rekor transparency log inclusion, OIDC identity,
+    /// and source repository via CertificateExtensionPolicy.
     /// </summary>
-    /// <returns><c>null</c> if verification succeeded; otherwise a failure result.</returns>
-    private async Task<ProvenanceVerificationResult?> VerifySigstoreBundleAsync(
-        JsonNode bundleNode,
+    /// <returns>A failure result and null verification result on error; null failure and the verification result on success.</returns>
+    private async Task<(ProvenanceVerificationResult? Failure, VerificationResult? Result)> VerifySigstoreBundleAsync(
+        SigstoreBundle bundle,
         string expectedSourceRepository,
         string? sriIntegrity,
         string packageName,
         string version,
         CancellationToken cancellationToken)
     {
-        var bundleJson = bundleNode.ToJsonString();
-        SigstoreBundle bundle;
-        try
-        {
-            bundle = SigstoreBundle.Deserialize(bundleJson);
-        }
-        catch (Exception ex)
-        {
-            logger.LogDebug(ex, "Failed to deserialize Sigstore bundle for {Package}@{Version}", packageName, version);
-            return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed };
-        }
-
         if (!TryParseGitHubOwnerRepo(expectedSourceRepository, out var owner, out var repo))
         {
             logger.LogWarning("Could not parse GitHub owner/repo from expected source repository: {ExpectedSourceRepository}", expectedSourceRepository);
-            return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.SourceRepositoryMismatch };
+            return (new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.SourceRepositoryMismatch }, null);
         }
 
         var verifier = new SigstoreVerifier();
@@ -268,16 +214,14 @@ internal static NpmAttestationParseResult ParseAttestation(string attestationJso
             }
             else
             {
-                var payloadBase64 = bundleNode["dsseEnvelope"]?["payload"]?.GetValue<string>();
-                if (payloadBase64 is null)
+                if (bundle.DsseEnvelope is null)
                 {
-                    logger.LogDebug("No DSSE payload found in bundle for {Package}@{Version}", packageName, version);
-                    return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.PayloadDecodeFailed };
+                    logger.LogDebug("No DSSE envelope found in bundle for {Package}@{Version}", packageName, version);
+                    return (new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.PayloadDecodeFailed }, null);
                 }
 
-                var payloadBytes = Convert.FromBase64String(payloadBase64);
                 (success, result) = await verifier.TryVerifyAsync(
-                    payloadBytes, bundle, policy, cancellationToken).ConfigureAwait(false);
+                    bundle.DsseEnvelope.Payload, bundle, policy, cancellationToken).ConfigureAwait(false);
             }
 
             if (!success)
@@ -285,25 +229,106 @@ internal static NpmAttestationParseResult ParseAttestation(string attestationJso
                 logger.LogWarning(
                     "Sigstore verification failed for {Package}@{Version}: {FailureReason}",
                     packageName, version, result?.FailureReason);
-                return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed };
+                return (new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed }, null);
             }
 
             logger.LogDebug(
                 "Sigstore verification passed for {Package}@{Version}. Signed by: {Signer}",
                 packageName, version, result?.SignerIdentity?.SubjectAlternativeName);
 
-            return null;
+            return (null, result);
         }
         catch (Exception ex)
         {
             logger.LogWarning(ex, "Sigstore verification threw an exception for {Package}@{Version}", packageName, version);
-            return new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed };
+            return (new ProvenanceVerificationResult { Outcome = ProvenanceVerificationOutcome.AttestationParseFailed }, null);
+        }
+    }
+
+    /// <summary>
+    /// Extracts provenance data from a verified Sigstore result using the in-toto statement
+    /// and Fulcio certificate extensions, avoiding manual JSON parsing of the DSSE payload.
+    /// </summary>
+    internal static NpmProvenanceData? ExtractProvenanceFromResult(VerificationResult result)
+    {
+        var extensions = result.SignerIdentity?.Extensions;
+        var statement = result.Statement;
+
+        // Extract SLSA-specific fields from the in-toto statement predicate.
+        string? workflowPath = null;
+        string? buildType = null;
+        string? builderId = null;
+        string? sourceRepository = null;
+        string? workflowRef = null;
+
+        if (statement?.PredicateType == SlsaProvenancePredicateType && statement.Predicate is { } predicate)
+        {
+            if (predicate.ValueKind == JsonValueKind.Object)
+            {
+                if (predicate.TryGetProperty("buildDefinition", out var buildDefinition) &&
+                    buildDefinition.ValueKind == JsonValueKind.Object)
+                {
+                    if (buildDefinition.TryGetProperty("buildType", out var buildTypeElement) &&
+                        buildTypeElement.ValueKind == JsonValueKind.String)
+                    {
+                        buildType = buildTypeElement.GetString();
+                    }
+
+                    if (buildDefinition.TryGetProperty("externalParameters", out var extParams) &&
+                        extParams.ValueKind == JsonValueKind.Object &&
+                        extParams.TryGetProperty("workflow", out var workflow) &&
+                        workflow.ValueKind == JsonValueKind.Object)
+                    {
+                        if (workflow.TryGetProperty("repository", out var repoEl) &&
+                            repoEl.ValueKind == JsonValueKind.String)
+                        {
+                            sourceRepository = repoEl.GetString();
+                        }
+
+                        if (workflow.TryGetProperty("path", out var pathEl) &&
+                            pathEl.ValueKind == JsonValueKind.String)
+                        {
+                            workflowPath = pathEl.GetString();
+                        }
+
+                        if (workflow.TryGetProperty("ref", out var refEl) &&
+                            refEl.ValueKind == JsonValueKind.String)
+                        {
+                            workflowRef = refEl.GetString();
+                        }
+                    }
+                }
+
+                if (predicate.TryGetProperty("runDetails", out var runDetails) &&
+                    runDetails.ValueKind == JsonValueKind.Object &&
+                    runDetails.TryGetProperty("builder", out var builder) &&
+                    builder.ValueKind == JsonValueKind.Object)
+                {
+                    if (builder.TryGetProperty("id", out var idEl) &&
+                        idEl.ValueKind == JsonValueKind.String)
+                    {
+                        builderId = idEl.GetString();
+                    }
+                }
+            }
         }
+
+        // Prefer certificate extensions for source repository and ref when available,
+        // as they are cryptographically bound to the signing certificate.
+        return new NpmProvenanceData
+        {
+            SourceRepository = extensions?.SourceRepositoryUri ?? sourceRepository,
+            WorkflowPath = workflowPath,
+            WorkflowRef = extensions?.SourceRepositoryRef ?? workflowRef,
+            BuilderId = builderId,
+            BuildType = buildType
+        };
     }
 
     /// <summary>
     /// Verifies that the extracted provenance fields match the expected values.
-    /// Checks source repository, workflow path, build type, and workflow ref in order.
+    /// Source repository is already verified cryptographically via CertificateExtensionPolicy
+    /// during Sigstore bundle verification, but is also checked here for defense-in-depth.
     /// </summary>
     internal static ProvenanceVerificationResult VerifyProvenanceFields(
         NpmProvenanceData provenance,
diff --git a/tests/Aspire.Cli.Tests/Agents/NpmProvenanceCheckerTests.cs b/tests/Aspire.Cli.Tests/Agents/NpmProvenanceCheckerTests.cs
deleted file mode 100644
index a6368649911..00000000000
--- a/tests/Aspire.Cli.Tests/Agents/NpmProvenanceCheckerTests.cs
+++ /dev/null
@@ -1,308 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Text;
-using System.Text.Json;
-using System.Text.Json.Nodes;
-using Aspire.Cli.Npm;
-
-namespace Aspire.Cli.Tests.Agents;
-
-public class NpmProvenanceCheckerTests
-{
-    [Fact]
-    public void ParseProvenance_WithValidSlsaProvenance_ReturnsVerifiedWithData()
-    {
-        var json = BuildAttestationJson("https://github.com/microsoft/playwright-cli");
-
-        var result = NpmProvenanceChecker.ParseProvenance(json);
-
-        Assert.NotNull(result);
-        Assert.Equal(ProvenanceVerificationOutcome.Verified, result.Value.Outcome);
-        Assert.Equal("https://github.com/microsoft/playwright-cli", result.Value.Provenance.SourceRepository);
-        Assert.Equal(".github/workflows/publish.yml", result.Value.Provenance.WorkflowPath);
-        Assert.Equal("https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1", result.Value.Provenance.BuildType);
-        Assert.Equal("https://github.com/actions/runner/github-hosted", result.Value.Provenance.BuilderId);
-        Assert.Equal("refs/tags/v0.1.1", result.Value.Provenance.WorkflowRef);
-    }
-
-    [Fact]
-    public void ParseProvenance_WithDifferentRepository_ReturnsVerifiedWithThatRepository()
-    {
-        var json = BuildAttestationJson("https://github.com/attacker/malicious-package");
-
-        var result = NpmProvenanceChecker.ParseProvenance(json);
-
-        Assert.NotNull(result);
-        Assert.Equal(ProvenanceVerificationOutcome.Verified, result.Value.Outcome);
-        Assert.Equal("https://github.com/attacker/malicious-package", result.Value.Provenance.SourceRepository);
-    }
-
-    [Fact]
-    public void ParseProvenance_WithNoSlsaPredicate_ReturnsSlsaProvenanceNotFound()
-    {
-        var json = """
-        {
-            "attestations": [
-                {
-                    "predicateType": "https://github.com/npm/attestation/tree/main/specs/publish/v0.1",
-                    "bundle": {
-                        "dsseEnvelope": {
-                            "payload": ""
-                        }
-                    }
-                }
-            ]
-        }
-        """;
-
-        var result = NpmProvenanceChecker.ParseProvenance(json);
-
-        Assert.NotNull(result);
-        Assert.Equal(ProvenanceVerificationOutcome.SlsaProvenanceNotFound, result.Value.Outcome);
-    }
-
-    [Fact]
-    public void ParseProvenance_WithEmptyAttestations_ReturnsSlsaProvenanceNotFound()
-    {
-        var json = """{"attestations": []}""";
-
-        var result = NpmProvenanceChecker.ParseProvenance(json);
-
-        Assert.NotNull(result);
-        Assert.Equal(ProvenanceVerificationOutcome.SlsaProvenanceNotFound, result.Value.Outcome);
-    }
-
-    [Fact]
-    public void ParseProvenance_WithMalformedJson_ThrowsException()
-    {
-        Assert.ThrowsAny<JsonException>(() => NpmProvenanceChecker.ParseProvenance("not json"));
-    }
-
-    [Fact]
-    public void ParseProvenance_WithMissingWorkflowNode_ReturnsSourceRepositoryNotFound()
-    {
-        var statement = new JsonObject
-        {
-            ["_type"] = "https://in-toto.io/Statement/v1",
-            ["predicateType"] = "https://slsa.dev/provenance/v1",
-            ["predicate"] = new JsonObject
-            {
-                ["buildDefinition"] = new JsonObject
-                {
-                    ["externalParameters"] = new JsonObject()
-                }
-            }
-        };
-
-        var payload = Convert.ToBase64String(Encoding.UTF8.GetBytes(statement.ToJsonString()));
-        var json = $$"""
-        {
-            "attestations": [
-                {
-                    "predicateType": "https://slsa.dev/provenance/v1",
-                    "bundle": {
-                        "dsseEnvelope": {
-                            "payload": "{{payload}}"
-                        }
-                    }
-                }
-            ]
-        }
-        """;
-
-        var result = NpmProvenanceChecker.ParseProvenance(json);
-
-        Assert.NotNull(result);
-        Assert.Equal(ProvenanceVerificationOutcome.SourceRepositoryNotFound, result.Value.Outcome);
-    }
-
-    [Fact]
-    public void ParseProvenance_WithMissingPayload_ReturnsPayloadDecodeFailed()
-    {
-        var json = """
-        {
-            "attestations": [
-                {
-                    "predicateType": "https://slsa.dev/provenance/v1",
-                    "bundle": {
-                        "dsseEnvelope": {}
-                    }
-                }
-            ]
-        }
-        """;
-
-        var result = NpmProvenanceChecker.ParseProvenance(json);
-
-        Assert.NotNull(result);
-        Assert.Equal(ProvenanceVerificationOutcome.PayloadDecodeFailed, result.Value.Outcome);
-    }
-
-    [Fact]
-    public async Task VerifyProvenanceAsync_WithMismatchedWorkflowRef_ReturnsWorkflowRefMismatch()
-    {
-        var json = BuildAttestationJson(
-            "https://github.com/microsoft/playwright-cli",
-            workflowRef: "refs/tags/v9.9.9");
-
-        var handler = new TestHttpMessageHandler(json);
-        var httpClient = new HttpClient(handler);
-        var checker = new NpmProvenanceChecker(httpClient, Microsoft.Extensions.Logging.Abstractions.NullLogger<NpmProvenanceChecker>.Instance);
-
-        var result = await checker.VerifyProvenanceAsync(
-            "@playwright/cli",
-            "0.1.1",
-            "https://github.com/microsoft/playwright-cli",
-            ".github/workflows/publish.yml",
-            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
-            refInfo => string.Equals(refInfo.Kind, "tags", StringComparison.Ordinal) &&
-                       string.Equals(refInfo.Name, "v0.1.1", StringComparison.Ordinal),
-            CancellationToken.None);
-
-        Assert.Equal(ProvenanceVerificationOutcome.WorkflowRefMismatch, result.Outcome);
-        Assert.Equal("refs/tags/v9.9.9", result.Provenance?.WorkflowRef);
-    }
-
-    [Fact]
-    public async Task VerifyProvenanceAsync_WithMatchingWorkflowRef_ReturnsVerified()
-    {
-        var json = BuildAttestationJson(
-            "https://github.com/microsoft/playwright-cli",
-            workflowRef: "refs/tags/v0.1.1");
-
-        var handler = new TestHttpMessageHandler(json);
-        var httpClient = new HttpClient(handler);
-        var checker = new NpmProvenanceChecker(httpClient, Microsoft.Extensions.Logging.Abstractions.NullLogger<NpmProvenanceChecker>.Instance);
-
-        var result = await checker.VerifyProvenanceAsync(
-            "@playwright/cli",
-            "0.1.1",
-            "https://github.com/microsoft/playwright-cli",
-            ".github/workflows/publish.yml",
-            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
-            refInfo => string.Equals(refInfo.Kind, "tags", StringComparison.Ordinal) &&
-                       string.Equals(refInfo.Name, "v0.1.1", StringComparison.Ordinal),
-            CancellationToken.None);
-
-        Assert.Equal(ProvenanceVerificationOutcome.Verified, result.Outcome);
-    }
-
-    [Fact]
-    public async Task VerifyProvenanceAsync_WithNullCallback_SkipsRefValidation()
-    {
-        var json = BuildAttestationJson(
-            "https://github.com/microsoft/playwright-cli",
-            workflowRef: "refs/tags/any-format-at-all");
-
-        var handler = new TestHttpMessageHandler(json);
-        var httpClient = new HttpClient(handler);
-        var checker = new NpmProvenanceChecker(httpClient, Microsoft.Extensions.Logging.Abstractions.NullLogger<NpmProvenanceChecker>.Instance);
-
-        var result = await checker.VerifyProvenanceAsync(
-            "@playwright/cli",
-            "0.1.1",
-            "https://github.com/microsoft/playwright-cli",
-            ".github/workflows/publish.yml",
-            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
-            validateWorkflowRef: null,
-            CancellationToken.None);
-
-        Assert.Equal(ProvenanceVerificationOutcome.Verified, result.Outcome);
-    }
-
-    private static string BuildAttestationJson(string sourceRepository, string workflowPath = ".github/workflows/publish.yml", string buildType = "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1", string workflowRef = "refs/tags/v0.1.1")
-    {
-        var statement = new JsonObject
-        {
-            ["_type"] = "https://in-toto.io/Statement/v1",
-            ["predicateType"] = "https://slsa.dev/provenance/v1",
-            ["predicate"] = new JsonObject
-            {
-                ["buildDefinition"] = new JsonObject
-                {
-                    ["buildType"] = buildType,
-                    ["externalParameters"] = new JsonObject
-                    {
-                        ["workflow"] = new JsonObject
-                        {
-                            ["repository"] = sourceRepository,
-                            ["path"] = workflowPath,
-                            ["ref"] = workflowRef
-                        }
-                    }
-                },
-                ["runDetails"] = new JsonObject
-                {
-                    ["builder"] = new JsonObject
-                    {
-                        ["id"] = "https://github.com/actions/runner/github-hosted"
-                    }
-                }
-            }
-        };
-
-        var payload = Convert.ToBase64String(Encoding.UTF8.GetBytes(statement.ToJsonString()));
-
-        var attestationResponse = new JsonObject
-        {
-            ["attestations"] = new JsonArray
-            {
-                new JsonObject
-                {
-                    ["predicateType"] = "https://slsa.dev/provenance/v1",
-                    ["bundle"] = new JsonObject
-                    {
-                        ["dsseEnvelope"] = new JsonObject
-                        {
-                            ["payload"] = payload
-                        }
-                    }
-                }
-            }
-        };
-
-        return attestationResponse.ToJsonString();
-    }
-
-    private sealed class TestHttpMessageHandler(string responseContent) : HttpMessageHandler
-    {
-        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
-        {
-            return Task.FromResult(new HttpResponseMessage(System.Net.HttpStatusCode.OK)
-            {
-                Content = new StringContent(responseContent, Encoding.UTF8, "application/json")
-            });
-        }
-    }
-
-    [Theory]
-    [InlineData("refs/tags/v0.1.1", "tags", "v0.1.1")]
-    [InlineData("refs/heads/main", "heads", "main")]
-    [InlineData("refs/tags/@scope/pkg@1.0.0", "tags", "@scope/pkg@1.0.0")]
-    [InlineData("refs/tags/release/1.0.0", "tags", "release/1.0.0")]
-    public void WorkflowRefInfo_TryParse_ValidRefs_ParsesCorrectly(string raw, string expectedKind, string expectedName)
-    {
-        var success = WorkflowRefInfo.TryParse(raw, out var refInfo);
-
-        Assert.True(success);
-        Assert.NotNull(refInfo);
-        Assert.Equal(raw, refInfo.Raw);
-        Assert.Equal(expectedKind, refInfo.Kind);
-        Assert.Equal(expectedName, refInfo.Name);
-    }
-
-    [Theory]
-    [InlineData(null)]
-    [InlineData("")]
-    [InlineData("not-a-ref")]
-    [InlineData("refs/")]
-    [InlineData("refs/tags/")]
-    public void WorkflowRefInfo_TryParse_InvalidRefs_ReturnsFalse(string? raw)
-    {
-        var success = WorkflowRefInfo.TryParse(raw, out var refInfo);
-
-        Assert.False(success);
-        Assert.Null(refInfo);
-    }
-}
diff --git a/tests/Aspire.Cli.Tests/Agents/SigstoreNpmProvenanceCheckerTests.cs b/tests/Aspire.Cli.Tests/Agents/SigstoreNpmProvenanceCheckerTests.cs
index c0a6541e9fb..3f8c063a81f 100644
--- a/tests/Aspire.Cli.Tests/Agents/SigstoreNpmProvenanceCheckerTests.cs
+++ b/tests/Aspire.Cli.Tests/Agents/SigstoreNpmProvenanceCheckerTests.cs
@@ -1,30 +1,30 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Text.Json;
 using Aspire.Cli.Npm;
+using Sigstore;
 
 namespace Aspire.Cli.Tests.Agents;
 
 public class SigstoreNpmProvenanceCheckerTests
 {
+    #region ExtractSlsaBundleJson Tests
+
     [Fact]
-    public void ParseAttestation_WithValidSlsaAttestation_ReturnsBundleAndProvenance()
+    public void ExtractSlsaBundleJson_WithValidSlsaAttestation_ReturnsBundleJson()
     {
         var json = BuildAttestationJsonWithBundle("https://github.com/microsoft/playwright-cli");
 
-        var result = SigstoreNpmProvenanceChecker.ParseAttestation(json);
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
 
-        Assert.Equal(ProvenanceVerificationOutcome.Verified, result.Outcome);
-        Assert.NotNull(result.BundleNode);
-        Assert.NotNull(result.BundleNode["dsseEnvelope"]);
-        Assert.NotNull(result.Provenance);
-        Assert.Equal("https://github.com/microsoft/playwright-cli", result.Provenance.SourceRepository);
-        Assert.Equal(".github/workflows/publish.yml", result.Provenance.WorkflowPath);
-        Assert.Equal("refs/tags/v0.1.1", result.Provenance.WorkflowRef);
+        Assert.NotNull(bundleJson);
+        var bundleDoc = JsonDocument.Parse(bundleJson);
+        Assert.True(bundleDoc.RootElement.TryGetProperty("dsseEnvelope", out _));
     }
 
     [Fact]
-    public void ParseAttestation_WithNoSlsaPredicate_ReturnsSlsaProvenanceNotFound()
+    public void ExtractSlsaBundleJson_WithNoSlsaPredicate_ReturnsNull()
     {
         var json = """
         {
@@ -41,58 +41,89 @@ public void ParseAttestation_WithNoSlsaPredicate_ReturnsSlsaProvenanceNotFound()
         }
         """;
 
-        var result = SigstoreNpmProvenanceChecker.ParseAttestation(json);
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
 
-        Assert.Equal(ProvenanceVerificationOutcome.SlsaProvenanceNotFound, result.Outcome);
+        Assert.Null(bundleJson);
     }
 
     [Fact]
-    public void ParseAttestation_WithEmptyAttestations_ReturnsSlsaProvenanceNotFound()
+    public void ExtractSlsaBundleJson_WithEmptyAttestations_ReturnsNull()
     {
-        var json = """{"attestations": []}""";
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson("""{"attestations": []}""", out _);
 
-        var result = SigstoreNpmProvenanceChecker.ParseAttestation(json);
-
-        Assert.Equal(ProvenanceVerificationOutcome.SlsaProvenanceNotFound, result.Outcome);
+        Assert.Null(bundleJson);
     }
 
     [Fact]
-    public void ParseAttestation_WithInvalidJson_ReturnsAttestationParseFailed()
+    public void ExtractSlsaBundleJson_WithInvalidJson_ReturnsNullAndSetsParseFailed()
     {
-        var result = SigstoreNpmProvenanceChecker.ParseAttestation("not valid json {{{");
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson("not valid json {{{", out var parseFailed);
 
-        Assert.Equal(ProvenanceVerificationOutcome.AttestationParseFailed, result.Outcome);
+        Assert.Null(bundleJson);
+        Assert.True(parseFailed);
     }
 
     [Fact]
-    public void ParseAttestation_WithMissingPayload_ReturnsPayloadDecodeFailed()
+    public void ExtractSlsaBundleJson_WithMultipleMixedAttestations_FindsSlsaPredicate()
     {
-        var json = """
+        var json = $$"""
         {
             "attestations": [
+                {
+                    "predicateType": "https://github.com/npm/attestation/tree/main/specs/publish/v0.1",
+                    "bundle": { "wrong": true }
+                },
                 {
                     "predicateType": "https://slsa.dev/provenance/v1",
                     "bundle": {
-                        "dsseEnvelope": {}
+                        "dsseEnvelope": { "payload": "dGVzdA==", "payloadType": "application/vnd.in-toto+json" }
                     }
                 }
             ]
         }
         """;
 
-        var result = SigstoreNpmProvenanceChecker.ParseAttestation(json);
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
 
-        Assert.Equal(ProvenanceVerificationOutcome.PayloadDecodeFailed, result.Outcome);
-        Assert.NotNull(result.BundleNode);
+        Assert.NotNull(bundleJson);
+        var doc = JsonDocument.Parse(bundleJson);
+        Assert.True(doc.RootElement.TryGetProperty("dsseEnvelope", out _));
     }
 
     [Fact]
-    public void ParseProvenanceFromStatement_WithValidStatement_ReturnsProvenance()
+    public void ExtractSlsaBundleJson_WithNoBundleProperty_ReturnsNull()
     {
-        var payload = BuildProvenancePayload("https://github.com/microsoft/playwright-cli");
-        var bytes = System.Text.Encoding.UTF8.GetBytes(payload);
+        var json = """
+        {
+            "attestations": [
+                {
+                    "predicateType": "https://slsa.dev/provenance/v1"
+                }
+            ]
+        }
+        """;
 
-        var provenance = SigstoreNpmProvenanceChecker.ParseProvenanceFromStatement(bytes);
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
+
+        Assert.Null(bundleJson);
+    }
+
+    #endregion
+
+    #region ExtractProvenanceFromResult Tests
+
+    [Fact]
+    public void ExtractProvenanceFromResult_WithStatementAndExtensions_ReturnsProvenance()
+    {
+        var result = BuildVerificationResult(
+            sourceRepoUri: "https://github.com/microsoft/playwright-cli",
+            sourceRepoRef: "refs/tags/v0.1.1",
+            workflowPath: ".github/workflows/publish.yml",
+            buildType: "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            builderId: "https://github.com/actions/runner/github-hosted",
+            sourceRepoInPredicate: "https://github.com/microsoft/playwright-cli");
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
 
         Assert.NotNull(provenance);
         Assert.Equal("https://github.com/microsoft/playwright-cli", provenance.SourceRepository);
@@ -103,15 +134,109 @@ public void ParseProvenanceFromStatement_WithValidStatement_ReturnsProvenance()
     }
 
     [Fact]
-    public void ParseProvenanceFromStatement_WithInvalidJson_ReturnsNull()
+    public void ExtractProvenanceFromResult_PrefersExtensionsOverPredicate()
+    {
+        var result = BuildVerificationResult(
+            sourceRepoUri: "https://github.com/microsoft/playwright-cli",
+            sourceRepoRef: "refs/tags/v0.1.1",
+            workflowPath: ".github/workflows/publish.yml",
+            buildType: "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            builderId: "https://github.com/actions/runner/github-hosted",
+            sourceRepoInPredicate: "https://github.com/evil/repo",
+            workflowRefInPredicate: "refs/heads/main");
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
+
+        Assert.NotNull(provenance);
+        // Certificate extensions should win over predicate values
+        Assert.Equal("https://github.com/microsoft/playwright-cli", provenance.SourceRepository);
+        Assert.Equal("refs/tags/v0.1.1", provenance.WorkflowRef);
+    }
+
+    [Fact]
+    public void ExtractProvenanceFromResult_WithNoStatement_ReturnsPartialProvenance()
     {
-        var bytes = System.Text.Encoding.UTF8.GetBytes("not json");
+        var result = new VerificationResult
+        {
+            SignerIdentity = new VerifiedIdentity
+            {
+                SubjectAlternativeName = "https://github.com/microsoft/playwright-cli/.github/workflows/publish.yml@refs/tags/v0.1.1",
+                Issuer = "https://token.actions.githubusercontent.com",
+                Extensions = new FulcioCertificateExtensions
+                {
+                    SourceRepositoryUri = "https://github.com/microsoft/playwright-cli",
+                    SourceRepositoryRef = "refs/tags/v0.1.1"
+                }
+            },
+            Statement = null
+        };
 
-        var provenance = SigstoreNpmProvenanceChecker.ParseProvenanceFromStatement(bytes);
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
 
-        Assert.Null(provenance);
+        Assert.NotNull(provenance);
+        Assert.Equal("https://github.com/microsoft/playwright-cli", provenance.SourceRepository);
+        Assert.Equal("refs/tags/v0.1.1", provenance.WorkflowRef);
+        Assert.Null(provenance.WorkflowPath);
+        Assert.Null(provenance.BuildType);
+        Assert.Null(provenance.BuilderId);
     }
 
+    [Fact]
+    public void ExtractProvenanceFromResult_WithNoExtensions_FallsToPredicate()
+    {
+        var result = BuildVerificationResult(
+            sourceRepoUri: null,
+            sourceRepoRef: null,
+            workflowPath: ".github/workflows/publish.yml",
+            buildType: "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            builderId: "https://github.com/actions/runner/github-hosted",
+            sourceRepoInPredicate: "https://github.com/microsoft/playwright-cli",
+            workflowRefInPredicate: "refs/tags/v0.1.1",
+            includeExtensions: false);
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
+
+        Assert.NotNull(provenance);
+        Assert.Equal("https://github.com/microsoft/playwright-cli", provenance.SourceRepository);
+        Assert.Equal("refs/tags/v0.1.1", provenance.WorkflowRef);
+    }
+
+    [Fact]
+    public void ExtractProvenanceFromResult_WithWrongPredicateType_ReturnsNullFields()
+    {
+        var predicateJson = """
+        {
+            "_type": "https://in-toto.io/Statement/v1",
+            "predicateType": "https://example.com/custom/v1",
+            "subject": [],
+            "predicate": { "custom": true }
+        }
+        """;
+
+        var statement = InTotoStatement.Parse(predicateJson);
+        var result = new VerificationResult
+        {
+            SignerIdentity = new VerifiedIdentity
+            {
+                SubjectAlternativeName = "test",
+                Issuer = "test",
+                Extensions = new FulcioCertificateExtensions()
+            },
+            Statement = statement
+        };
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
+
+        Assert.NotNull(provenance);
+        Assert.Null(provenance.WorkflowPath);
+        Assert.Null(provenance.BuildType);
+        Assert.Null(provenance.BuilderId);
+    }
+
+    #endregion
+
+    #region VerifyProvenanceFields Tests
+
     [Fact]
     public void VerifyProvenanceFields_WithAllFieldsMatching_ReturnsVerified()
     {
@@ -215,6 +340,10 @@ public void VerifyProvenanceFields_WithWorkflowRefValidationFailure_ReturnsWorkf
         Assert.Equal(ProvenanceVerificationOutcome.WorkflowRefMismatch, result.Outcome);
     }
 
+    #endregion
+
+    #region TryParseGitHubOwnerRepo Tests
+
     [Theory]
     [InlineData("https://github.com/microsoft/playwright-cli", "microsoft", "playwright-cli")]
     [InlineData("https://github.com/dotnet/aspire", "dotnet", "aspire")]
@@ -239,9 +368,634 @@ public void TryParseGitHubOwnerRepo_WithInvalidUrl_ReturnsFalse(string url)
         Assert.False(result);
     }
 
+    #endregion
+
+    #region Adversarial Tests - Malformed JSON
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithDeeplyNestedJson_ReturnsNull()
+    {
+        // Build a valid deeply-nested JSON object to test stack safety.
+        // Each level wraps the previous in {"key": ...}.
+        var depth = 200;
+        var inner = """{"attestations":[]}""";
+        for (var i = 0; i < depth; i++)
+        {
+            inner = $$"""{"level{{i}}":{{inner}}}""";
+        }
+
+        // Should either return null or handle gracefully (no exception)
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(inner, out _);
+
+        // The deeply nested JSON has "attestations" buried inside — not at root level
+        Assert.Null(bundleJson);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithTruncatedJson_ReturnsNull()
+    {
+        var json = """{"attestations": [{"predicateType": "https://slsa.dev/provenance/v1", "bundle": {"dsse""";
+
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
+
+        Assert.Null(bundleJson);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithWrongJsonTypes_ReturnsNull()
+    {
+        // attestations is a string instead of array
+        var json = """{"attestations": "not an array"}""";
+
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
+
+        Assert.Null(bundleJson);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithNullAttestations_ReturnsNull()
+    {
+        var json = """{"attestations": null}""";
+
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
+
+        Assert.Null(bundleJson);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithEmptyObject_ReturnsNullWithoutParseFailed()
+    {
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson("{}", out var parseFailed);
+
+        Assert.Null(bundleJson);
+        Assert.False(parseFailed);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithNonObjectArrayElements_SkipsThem()
+    {
+        // Array contains string, number, and null elements instead of objects
+        var json = """
+        {
+            "attestations": [
+                "not an object",
+                42,
+                null,
+                {
+                    "predicateType": "https://slsa.dev/provenance/v1",
+                    "bundle": { "dsseEnvelope": {} }
+                }
+            ]
+        }
+        """;
+
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out var parseFailed);
+
+        Assert.NotNull(bundleJson);
+        Assert.False(parseFailed);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithNonStringPredicateType_SkipsElement()
+    {
+        // predicateType is a number instead of a string
+        var json = """
+        {
+            "attestations": [
+                {
+                    "predicateType": 42,
+                    "bundle": { "dsseEnvelope": {} }
+                }
+            ]
+        }
+        """;
+
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out var parseFailed);
+
+        Assert.Null(bundleJson);
+        Assert.False(parseFailed);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithEmptyString_ReturnsNullAndSetsParseFailed()
+    {
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson("", out var parseFailed);
+
+        Assert.Null(bundleJson);
+        Assert.True(parseFailed);
+    }
+
+    #endregion
+
+    #region Adversarial Tests - Provenance Spoofing
+
+    [Theory]
+    [InlineData("https://github.com/micr0soft/playwright-cli")] // Homoglyph: zero instead of 'o'
+    [InlineData("https://github.com/microsofт/playwright-cli")] // Homoglyph: Turkish dotless t
+    [InlineData("https://github.com/microsoft-/playwright-cli")] // Trailing dash
+    [InlineData("https://github.com/MICROSOFT/playwright-cli")] // Case should match (OrdinalIgnoreCase)
+    public void VerifyProvenanceFields_WithSimilarRepositoryUrls_ChecksCorrectly(string spoofedUrl)
+    {
+        var provenance = new NpmProvenanceData
+        {
+            SourceRepository = spoofedUrl,
+            WorkflowPath = ".github/workflows/publish.yml",
+            BuildType = "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+        };
+
+        var result = SigstoreNpmProvenanceChecker.VerifyProvenanceFields(
+            provenance,
+            "https://github.com/microsoft/playwright-cli",
+            ".github/workflows/publish.yml",
+            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            null);
+
+        // MICROSOFT should match (OrdinalIgnoreCase), all others should fail
+        if (string.Equals(spoofedUrl, "https://github.com/microsoft/playwright-cli", StringComparison.OrdinalIgnoreCase))
+        {
+            Assert.Equal(ProvenanceVerificationOutcome.Verified, result.Outcome);
+        }
+        else
+        {
+            Assert.Equal(ProvenanceVerificationOutcome.SourceRepositoryMismatch, result.Outcome);
+        }
+    }
+
+    [Theory]
+    [InlineData("../../.github/workflows/evil.yml")]
+    [InlineData(".github/workflows/../../../evil.yml")]
+    [InlineData(".github/workflows/publish.yml\0evil")]
+    [InlineData("")]
+    public void VerifyProvenanceFields_WithWorkflowPathManipulation_RejectsInvalid(string spoofedPath)
+    {
+        var provenance = new NpmProvenanceData
+        {
+            SourceRepository = "https://github.com/microsoft/playwright-cli",
+            WorkflowPath = spoofedPath,
+            BuildType = "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+        };
+
+        var result = SigstoreNpmProvenanceChecker.VerifyProvenanceFields(
+            provenance,
+            "https://github.com/microsoft/playwright-cli",
+            ".github/workflows/publish.yml",
+            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            null);
+
+        Assert.Equal(ProvenanceVerificationOutcome.WorkflowMismatch, result.Outcome);
+    }
+
+    [Theory]
+    [InlineData("refs/heads/main")] // Branch instead of tag
+    [InlineData("refs/tags/v0.1.1/../../heads/main")] // Path traversal in ref
+    [InlineData("refs/tags/")] // Empty tag name
+    [InlineData("refs/")] // No kind or name
+    [InlineData("tags/v0.1.1")] // Missing refs/ prefix
+    [InlineData("")] // Empty string
+    public void VerifyProvenanceFields_WithRefManipulation_RejectsInvalidRefs(string spoofedRef)
+    {
+        var provenance = new NpmProvenanceData
+        {
+            SourceRepository = "https://github.com/microsoft/playwright-cli",
+            WorkflowPath = ".github/workflows/publish.yml",
+            BuildType = "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            WorkflowRef = spoofedRef
+        };
+
+        var result = SigstoreNpmProvenanceChecker.VerifyProvenanceFields(
+            provenance,
+            "https://github.com/microsoft/playwright-cli",
+            ".github/workflows/publish.yml",
+            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            refInfo => string.Equals(refInfo.Kind, "tags", StringComparison.Ordinal) &&
+                       string.Equals(refInfo.Name, "v0.1.1", StringComparison.Ordinal));
+
+        Assert.Equal(ProvenanceVerificationOutcome.WorkflowRefMismatch, result.Outcome);
+    }
+
+    [Fact]
+    public void VerifyProvenanceFields_WithNullWorkflowRef_ReturnsWorkflowRefMismatch()
+    {
+        var provenance = new NpmProvenanceData
+        {
+            SourceRepository = "https://github.com/microsoft/playwright-cli",
+            WorkflowPath = ".github/workflows/publish.yml",
+            BuildType = "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            WorkflowRef = null
+        };
+
+        var result = SigstoreNpmProvenanceChecker.VerifyProvenanceFields(
+            provenance,
+            "https://github.com/microsoft/playwright-cli",
+            ".github/workflows/publish.yml",
+            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            refInfo => refInfo.Kind == "tags");
+
+        Assert.Equal(ProvenanceVerificationOutcome.WorkflowRefMismatch, result.Outcome);
+    }
+
+    #endregion
+
+    #region Adversarial Tests - Build Type Spoofing
+
+    [Theory]
+    [InlineData("https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1?inject=true")]
+    [InlineData("https://evil.com/github-actions-buildtypes/workflow/v1")]
+    [InlineData("")]
+    public void VerifyProvenanceFields_WithBuildTypeSpoofing_Rejects(string spoofedBuildType)
+    {
+        var provenance = new NpmProvenanceData
+        {
+            SourceRepository = "https://github.com/microsoft/playwright-cli",
+            WorkflowPath = ".github/workflows/publish.yml",
+            BuildType = spoofedBuildType,
+        };
+
+        var result = SigstoreNpmProvenanceChecker.VerifyProvenanceFields(
+            provenance,
+            "https://github.com/microsoft/playwright-cli",
+            ".github/workflows/publish.yml",
+            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            null);
+
+        Assert.Equal(ProvenanceVerificationOutcome.BuildTypeMismatch, result.Outcome);
+    }
+
+    [Fact]
+    public void VerifyProvenanceFields_WithNullBuildType_ReturnsBuildTypeMismatch()
+    {
+        var provenance = new NpmProvenanceData
+        {
+            SourceRepository = "https://github.com/microsoft/playwright-cli",
+            WorkflowPath = ".github/workflows/publish.yml",
+            BuildType = null,
+        };
+
+        var result = SigstoreNpmProvenanceChecker.VerifyProvenanceFields(
+            provenance,
+            "https://github.com/microsoft/playwright-cli",
+            ".github/workflows/publish.yml",
+            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            null);
+
+        Assert.Equal(ProvenanceVerificationOutcome.BuildTypeMismatch, result.Outcome);
+    }
+
+    #endregion
+
+    #region Adversarial Tests - URL Parsing Edge Cases
+
+    [Theory]
+    [InlineData("https://github.com.evil.com/microsoft/playwright-cli")] // Subdomain attack
+    [InlineData("https://githüb.com/microsoft/playwright-cli")] // Unicode domain
+    [InlineData("ftp://github.com/microsoft/playwright-cli")] // Wrong scheme
+    public void TryParseGitHubOwnerRepo_WithSuspiciousUrls_HandlesCorrectly(string url)
+    {
+        var result = SigstoreNpmProvenanceChecker.TryParseGitHubOwnerRepo(url, out var owner, out var repo);
+
+        // These are syntactically valid URLs so TryParseGitHubOwnerRepo will succeed,
+        // but the domain mismatch would be caught by Sigstore's certificate identity check
+        // (SAN pattern matching against github.com). TryParseGitHubOwnerRepo only extracts
+        // the path segments — the security boundary is in the VerificationPolicy.
+        if (result)
+        {
+            // Verify it at least parsed the path segments
+            Assert.False(string.IsNullOrEmpty(owner));
+            Assert.False(string.IsNullOrEmpty(repo));
+        }
+    }
+
+    [Theory]
+    [InlineData("https://github.com/microsoft/playwright-cli/../evil-repo")]
+    [InlineData("https://github.com/microsoft/playwright-cli/extra/segments")]
+    public void TryParseGitHubOwnerRepo_WithExtraPathSegments_ExtractsFirstTwo(string url)
+    {
+        var result = SigstoreNpmProvenanceChecker.TryParseGitHubOwnerRepo(url, out var owner, out _);
+
+        Assert.True(result);
+        Assert.Equal("microsoft", owner);
+        // URI normalization resolves ".." so the path may differ
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData("   ")]
+    [InlineData("relative/path")]
+    public void TryParseGitHubOwnerRepo_WithNonAbsoluteUri_ReturnsFalse(string url)
+    {
+        var result = SigstoreNpmProvenanceChecker.TryParseGitHubOwnerRepo(url, out _, out _);
+
+        Assert.False(result);
+    }
+
+    #endregion
+
+    #region Adversarial Tests - Statement Extraction Edge Cases
+
+    [Fact]
+    public void ExtractProvenanceFromResult_WithMissingPredicateFields_ReturnsPartialData()
+    {
+        var predicateJson = """
+        {
+            "_type": "https://in-toto.io/Statement/v1",
+            "predicateType": "https://slsa.dev/provenance/v1",
+            "subject": [],
+            "predicate": {
+                "buildDefinition": {
+                    "buildType": "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1"
+                }
+            }
+        }
+        """;
+
+        var statement = InTotoStatement.Parse(predicateJson);
+        var result = new VerificationResult
+        {
+            SignerIdentity = new VerifiedIdentity
+            {
+                SubjectAlternativeName = "test",
+                Issuer = "test",
+                Extensions = new FulcioCertificateExtensions()
+            },
+            Statement = statement
+        };
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
+
+        Assert.NotNull(provenance);
+        Assert.Equal("https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1", provenance.BuildType);
+        Assert.Null(provenance.WorkflowPath);
+        Assert.Null(provenance.BuilderId);
+    }
+
+    [Fact]
+    public void ExtractProvenanceFromResult_WithEmptyPredicate_ReturnsNullFields()
+    {
+        var predicateJson = """
+        {
+            "_type": "https://in-toto.io/Statement/v1",
+            "predicateType": "https://slsa.dev/provenance/v1",
+            "subject": [],
+            "predicate": {}
+        }
+        """;
+
+        var statement = InTotoStatement.Parse(predicateJson);
+        var result = new VerificationResult
+        {
+            SignerIdentity = new VerifiedIdentity
+            {
+                SubjectAlternativeName = "test",
+                Issuer = "test",
+                Extensions = new FulcioCertificateExtensions()
+            },
+            Statement = statement
+        };
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
+
+        Assert.NotNull(provenance);
+        Assert.Null(provenance.BuildType);
+        Assert.Null(provenance.WorkflowPath);
+    }
+
+    [Fact]
+    public void ExtractProvenanceFromResult_WithNullSignerIdentity_ReturnsProvenanceFromPredicate()
+    {
+        var result = BuildVerificationResult(
+            sourceRepoUri: null,
+            sourceRepoRef: null,
+            workflowPath: ".github/workflows/publish.yml",
+            buildType: "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            builderId: "https://github.com/actions/runner/github-hosted",
+            sourceRepoInPredicate: "https://github.com/microsoft/playwright-cli",
+            includeIdentity: false);
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
+
+        Assert.NotNull(provenance);
+        Assert.Equal("https://github.com/microsoft/playwright-cli", provenance.SourceRepository);
+    }
+
+    #endregion
+
+    #region Adversarial Tests - Predicate Type Safety
+
+    [Fact]
+    public void ExtractProvenanceFromResult_WithWrongTypedPredicateValues_ReturnsNullFields()
+    {
+        // buildType is a number, workflow fields are arrays/booleans — all wrong types
+        var predicateJson = """
+        {
+            "_type": "https://in-toto.io/Statement/v1",
+            "predicateType": "https://slsa.dev/provenance/v1",
+            "subject": [],
+            "predicate": {
+                "buildDefinition": {
+                    "buildType": 42,
+                    "externalParameters": {
+                        "workflow": {
+                            "repository": true,
+                            "path": [],
+                            "ref": {}
+                        }
+                    }
+                },
+                "runDetails": {
+                    "builder": {
+                        "id": 999
+                    }
+                }
+            }
+        }
+        """;
+
+        var statement = InTotoStatement.Parse(predicateJson);
+        var result = new VerificationResult
+        {
+            SignerIdentity = new VerifiedIdentity
+            {
+                SubjectAlternativeName = "test",
+                Issuer = "test",
+                Extensions = new FulcioCertificateExtensions()
+            },
+            Statement = statement
+        };
+
+        var provenance = SigstoreNpmProvenanceChecker.ExtractProvenanceFromResult(result);
+
+        Assert.NotNull(provenance);
+        Assert.Null(provenance.BuildType);
+        Assert.Null(provenance.SourceRepository);
+        Assert.Null(provenance.WorkflowPath);
+        Assert.Null(provenance.WorkflowRef);
+        Assert.Null(provenance.BuilderId);
+    }
+
+    #endregion
+
+    #region Adversarial Tests - Attestation Structure
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithNullPredicateType_ReturnsNull()
+    {
+        var json = """
+        {
+            "attestations": [
+                {
+                    "bundle": { "dsseEnvelope": {} }
+                }
+            ]
+        }
+        """;
+
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
+
+        Assert.Null(bundleJson);
+    }
+
+    [Fact]
+    public void ExtractSlsaBundleJson_WithCaseSensitivePredicateType_ReturnsNull()
+    {
+        // Predicate type comparison is case-sensitive (Ordinal)
+        var json = """
+        {
+            "attestations": [
+                {
+                    "predicateType": "HTTPS://SLSA.DEV/PROVENANCE/V1",
+                    "bundle": { "dsseEnvelope": {} }
+                }
+            ]
+        }
+        """;
+
+        var bundleJson = SigstoreNpmProvenanceChecker.ExtractSlsaBundleJson(json, out _);
+
+        Assert.Null(bundleJson);
+    }
+
+    #endregion
+
+    #region WorkflowRefInfo Adversarial Tests
+
+    [Theory]
+    [InlineData("refs/tags/v1.0.0", true, "tags", "v1.0.0")]
+    [InlineData("refs/heads/main", true, "heads", "main")]
+    [InlineData("refs/tags/@scope/pkg@1.0.0", true, "tags", "@scope/pkg@1.0.0")]
+    [InlineData("refs/tags/", false, null, null)] // Empty name
+    [InlineData("refs/", false, null, null)] // No kind/name
+    [InlineData("", false, null, null)] // Empty string
+    [InlineData("heads/main", false, null, null)] // Missing refs/ prefix
+    [InlineData("refs/tags/v1/../../../etc/passwd", true, "tags", "v1/../../../etc/passwd")] // Path traversal in name (accepted as-is)
+    public void WorkflowRefInfo_TryParse_HandlesEdgeCases(string? input, bool expectedSuccess, string? expectedKind, string? expectedName)
+    {
+        var result = WorkflowRefInfo.TryParse(input, out var refInfo);
+
+        Assert.Equal(expectedSuccess, result);
+        if (expectedSuccess)
+        {
+            Assert.NotNull(refInfo);
+            Assert.Equal(expectedKind, refInfo.Kind);
+            Assert.Equal(expectedName, refInfo.Name);
+        }
+        else
+        {
+            Assert.Null(refInfo);
+        }
+    }
+
+    #endregion
+
+    #region Test Helpers
+
+    private static VerificationResult BuildVerificationResult(
+        string? sourceRepoUri,
+        string? sourceRepoRef,
+        string? workflowPath,
+        string? buildType,
+        string? builderId,
+        string? sourceRepoInPredicate = null,
+        string? workflowRefInPredicate = null,
+        bool includeExtensions = true,
+        bool includeIdentity = true)
+    {
+        var predicateJson = BuildSlsaPredicateStatementJson(
+            sourceRepoInPredicate ?? sourceRepoUri ?? "https://github.com/test/repo",
+            workflowPath ?? ".github/workflows/test.yml",
+            workflowRefInPredicate ?? sourceRepoRef ?? "refs/tags/v0.0.1",
+            buildType ?? "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            builderId ?? "https://github.com/actions/runner/github-hosted");
+
+        var statement = InTotoStatement.Parse(predicateJson);
+
+        VerifiedIdentity? identity = null;
+        if (includeIdentity)
+        {
+            identity = new VerifiedIdentity
+            {
+                SubjectAlternativeName = "https://github.com/test/repo/.github/workflows/test.yml@refs/tags/v0.0.1",
+                Issuer = "https://token.actions.githubusercontent.com",
+                Extensions = includeExtensions ? new FulcioCertificateExtensions
+                {
+                    SourceRepositoryUri = sourceRepoUri,
+                    SourceRepositoryRef = sourceRepoRef
+                } : null
+            };
+        }
+
+        return new VerificationResult
+        {
+            SignerIdentity = identity,
+            Statement = statement
+        };
+    }
+
+    private static string BuildSlsaPredicateStatementJson(
+        string sourceRepository,
+        string workflowPath,
+        string workflowRef,
+        string buildType,
+        string builderId)
+    {
+        return $$"""
+        {
+            "_type": "https://in-toto.io/Statement/v1",
+            "subject": [
+                {
+                    "name": "pkg:npm/@playwright/cli@0.1.1",
+                    "digest": { "sha512": "abc123" }
+                }
+            ],
+            "predicateType": "https://slsa.dev/provenance/v1",
+            "predicate": {
+                "buildDefinition": {
+                    "buildType": "{{buildType}}",
+                    "externalParameters": {
+                        "workflow": {
+                            "ref": "{{workflowRef}}",
+                            "repository": "{{sourceRepository}}",
+                            "path": "{{workflowPath}}"
+                        }
+                    }
+                },
+                "runDetails": {
+                    "builder": {
+                        "id": "{{builderId}}"
+                    }
+                }
+            }
+        }
+        """;
+    }
+
     private static string BuildAttestationJsonWithBundle(string sourceRepository)
     {
-        var payload = BuildProvenancePayload(sourceRepository);
+        var payload = BuildSlsaPredicateStatementJson(
+            sourceRepository,
+            ".github/workflows/publish.yml",
+            "refs/tags/v0.1.1",
+            "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
+            "https://github.com/actions/runner/github-hosted");
         var payloadBase64 = Convert.ToBase64String(System.Text.Encoding.UTF8.GetBytes(payload));
 
         return $$"""
@@ -290,36 +1044,5 @@ private static string BuildAttestationJsonWithBundle(string sourceRepository)
         """;
     }
 
-    private static string BuildProvenancePayload(string sourceRepository)
-    {
-        return $$"""
-        {
-            "_type": "https://in-toto.io/Statement/v1",
-            "subject": [
-                {
-                    "name": "pkg:npm/@playwright/cli@0.1.1",
-                    "digest": { "sha512": "abc123" }
-                }
-            ],
-            "predicateType": "https://slsa.dev/provenance/v1",
-            "predicate": {
-                "buildDefinition": {
-                    "buildType": "https://slsa-framework.github.io/github-actions-buildtypes/workflow/v1",
-                    "externalParameters": {
-                        "workflow": {
-                            "ref": "refs/tags/v0.1.1",
-                            "repository": "{{sourceRepository}}",
-                            "path": ".github/workflows/publish.yml"
-                        }
-                    }
-                },
-                "runDetails": {
-                    "builder": {
-                        "id": "https://github.com/actions/runner/github-hosted"
-                    }
-                }
-            }
-        }
-        """;
-    }
+    #endregion
 }