diff --git a/packages/provider-opencode/src/server/adapter.authentication.test.ts b/packages/provider-opencode/src/server/adapter.authentication.test.ts
new file mode 100644
index 0000000000000..65a55f559827e
--- /dev/null
+++ b/packages/provider-opencode/src/server/adapter.authentication.test.ts
@@ -0,0 +1,142 @@
+// @effect-diagnostics-next-line nodeBuiltinImport:off - The fixture rejects real SDK requests at the HTTP authentication boundary.
+import * as NodeHttp from "node:http";
+import * as NodeServices from "@effect/platform-node/NodeServices";
+import { assert, it } from "@effect/vitest";
+import { ProviderInstanceId, ProviderSessionId, ThreadId } from "@t3tools/contracts";
+import * as IdAllocator from "@t3tools/provider-core/server/IdAllocator";
+import * as McpProviderSessions from "@t3tools/provider-core/server/McpProviderSessions";
+import * as TestProviderHost from "@t3tools/provider-testing/TestProviderHost";
+import * as Effect from "effect/Effect";
+import * as Layer from "effect/Layer";
+import * as Schema from "effect/Schema";
+import * as ChildProcess from "effect/process/ChildProcess";
+import * as ChildProcessSpawner from "effect/process/ChildProcessSpawner";
+
+import { OpenCodeSettings } from "../settings.ts";
+import { makeOpenCodeAdapterV2 } from "./adapter.ts";
+import * as OpenCodeRuntime from "./OpenCodeRuntime.ts";
+import * as OpenCodeServerLedger from "./OpenCodeServerLedger.ts";
+
+const decodeSettings = Schema.decodeSync(OpenCodeSettings);
+
+it.live.each([true, false])("opens an authenticated OpenCode session (external=%s)", (external) =>
+  Effect.gen(function* () {
+    const password = external ? "settings-password" : "environment-password";
+    const requests: string[] = [];
+    let eventConnected!: () => void;
+    const eventRequest = new Promise<void>((resolve) => {
+      eventConnected = resolve;
+    });
+    const server = yield* Effect.acquireRelease(
+      Effect.promise(
+        () =>
+          new Promise<ReturnType<typeof NodeHttp.createServer>>((resolve) => {
+            const server = NodeHttp.createServer((request, response) => {
+              if (
+                request.headers.authorization !==
+                `Basic ${Buffer.from(`opencode:${password}`).toString("base64")}`
+              ) {
+                response.writeHead(401).end("Unauthorized");
+                return;
+              }
+              const url = new URL(request.url!, "http://localhost");
+              requests.push(url.pathname);
+              if (url.pathname === "/event") {
+                response.writeHead(200, { "Content-Type": "text/event-stream" });
+                response.write(": connected\n\n");
+                eventConnected();
+                return;
+              }
+              response.writeHead(200, { "Content-Type": "application/json" });
+              response.end(
+                JSON.stringify(
+                  url.pathname.endsWith("/children")
+                    ? []
+                    : url.pathname === "/session"
+                      ? { id: "native-auth", time: { created: 1, updated: 1 } }
+                      : { healthy: true, version: "1.14.19" },
+                ),
+              );
+            });
+            server.listen(0, "127.0.0.1", () => resolve(server));
+          }),
+      ),
+      (server) =>
+        Effect.promise(
+          () =>
+            new Promise<void>((resolve) => {
+              server.closeAllConnections();
+              server.close(() => resolve());
+            }),
+        ),
+    );
+    const address = server.address();
+    assert.isNotNull(address);
+    if (!address || typeof address === "string") return;
+    const url = `http://127.0.0.1:${address.port}`;
+    const spawner = yield* ChildProcessSpawner.ChildProcessSpawner;
+    let managedStarts = 0;
+    const runtimeLayer = OpenCodeRuntime.layer.pipe(
+      Layer.provide(
+        Layer.succeed(
+          ChildProcessSpawner.ChildProcessSpawner,
+          ChildProcessSpawner.make((command) => {
+            assert.isTrue(ChildProcess.isStandardCommand(command));
+            if (!ChildProcess.isStandardCommand(command)) return Effect.die("Unexpected pipeline");
+            assert.include(command.args, "serve");
+            assert.equal(command.options.env?.OPENCODE_SERVER_PASSWORD, password);
+            managedStarts += 1;
+            // Keep the real startup parser and process cleanup, replacing only the provider binary.
+            return spawner.spawn(
+              ChildProcess.make(
+                process.execPath,
+                [
+                  "-e",
+                  `console.log("server listening on " + process.argv[1]); setInterval(() => {}, 1000)`,
+                  url,
+                ],
+                command.options,
+              ),
+            );
+          }),
+        ),
+      ),
+      Layer.provide(OpenCodeServerLedger.layerTest),
+      Layer.provideMerge(NodeServices.layer),
+    );
+    const instanceId = ProviderInstanceId.make("opencode-auth");
+    const adapter = yield* makeOpenCodeAdapterV2({
+      instanceId,
+      settings: decodeSettings({
+        serverUrl: external ? url : "",
+        ...(external ? { serverPassword: password } : {}),
+      }),
+      environment: { OPENCODE_SERVER_PASSWORD: "environment-password" },
+    }).pipe(Effect.provide(runtimeLayer));
+    const session = yield* adapter.openSession({
+      threadId: ThreadId.make("thread-opencode-auth"),
+      providerSessionId: ProviderSessionId.make("session-opencode-auth"),
+      modelSelection: { instanceId, model: "anthropic/claude-sonnet", options: [] },
+      runtimePolicy: { runtimeMode: "full-access", interactionMode: "default", cwd: null },
+    });
+    yield* session.ensureThread({
+      threadId: ThreadId.make("thread-opencode-auth"),
+      modelSelection: { instanceId, model: "anthropic/claude-sonnet", options: [] },
+      runtimePolicy: { runtimeMode: "full-access", interactionMode: "default", cwd: null },
+    });
+    assert.equal(session.providerSessionId, "session-opencode-auth");
+    assert.include(requests, "/session");
+    yield* Effect.promise(() => eventRequest);
+    assert.include(requests, "/event");
+    assert.include(requests, "/global/health");
+    assert.equal(managedStarts, external ? 0 : 1);
+  }).pipe(
+    Effect.scoped,
+    Effect.provide([
+      NodeServices.layer,
+      TestProviderHost.layer().pipe(Layer.provide(NodeServices.layer)),
+      IdAllocator.layer,
+      McpProviderSessions.layer,
+    ]),
+  ),
+);
diff --git a/packages/provider-opencode/src/server/adapter.ts b/packages/provider-opencode/src/server/adapter.ts
index 9a6a6e265b205..28353935cffa1 100644
--- a/packages/provider-opencode/src/server/adapter.ts
+++ b/packages/provider-opencode/src/server/adapter.ts
@@ -945,13 +945,16 @@ export const makeOpenCodeAdapterV2 = Effect.fn("makeOpenCodeAdapterV2")(function
           binaryPath: options.settings.binaryPath,
           directory: cwd,
           serverUrl: options.settings.serverUrl,
+          ...(options.settings.serverPassword
+            ? { serverPassword: options.settings.serverPassword }
+            : {}),
           environment: options.environment,
         });
         const client = runtime.createOpenCodeSdkClient({
           baseUrl: connection.url,
           directory: cwd,
-          ...(connection.external && options.settings.serverPassword
-            ? { serverPassword: options.settings.serverPassword }
+          ...(connection.serverPassword !== undefined
+            ? { serverPassword: connection.serverPassword }
             : {}),
         });