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Add frameDomains and baseUriDomains CSP support for MCP Apps #6399

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Merged
aharvard merged 1 commit into from
Jan 9, 2026
Merged

Add frameDomains and baseUriDomains CSP support for MCP Apps #6399

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40 changes: 35 additions & 5 deletions crates/goose-server/src/routes/mcp_app_proxy.rs
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,10 @@ struct ProxyQuery {
connect_domains: Option<String>,
/// Comma-separated list of domains for resource loading (scripts, styles, images, fonts, media)
resource_domains: Option<String>,
/// Comma-separated list of origins for nested iframes (frame-src)
frame_domains: Option<String>,
/// Comma-separated list of allowed base URIs (base-uri)
base_uri_domains: Option<String>,
}

const MCP_APP_PROXY_HTML: &str = include_str!("templates/mcp_app_proxy.html");
Expand All @@ -26,7 +30,12 @@ const MCP_APP_PROXY_HTML: &str = include_str!("templates/mcp_app_proxy.html");
///
/// Based on the MCP Apps specification (ext-apps SEP):
/// <https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/draft/apps.mdx>
fn build_outer_csp(connect_domains: &[String], resource_domains: &[String]) -> String {
fn build_outer_csp(
connect_domains: &[String],
resource_domains: &[String],
frame_domains: &[String],
base_uri_domains: &[String],
) -> String {
let resources = if resource_domains.is_empty() {
String::new()
} else {
Expand All @@ -39,6 +48,18 @@ fn build_outer_csp(connect_domains: &[String], resource_domains: &[String]) -> S
format!(" {}", connect_domains.join(" "))
};

let frame_src = if frame_domains.is_empty() {
"frame-src 'none'".to_string()
} else {
format!("frame-src {}", frame_domains.join(" "))
};

let base_uris = if base_uri_domains.is_empty() {
String::new()
} else {
format!(" {}", base_uri_domains.join(" "))
};

format!(
"default-src 'none'; \
script-src 'self' 'unsafe-inline'{resources}; \
Expand All @@ -49,9 +70,9 @@ fn build_outer_csp(connect_domains: &[String], resource_domains: &[String]) -> S
img-src 'self' data: blob:{resources}; \
font-src 'self'{resources}; \
media-src 'self' data: blob:{resources}; \
frame-src blob: data:; \
{frame_src}; \
object-src 'none'; \
base-uri 'self'"
base-uri 'self'{base_uris}"
)
}

Expand All @@ -73,7 +94,9 @@ fn parse_domains(domains: Option<&String>) -> Vec<String> {
params(
("secret" = String, Query, description = "Secret key for authentication"),
("connect_domains" = Option<String>, Query, description = "Comma-separated domains for connect-src"),
("resource_domains" = Option<String>, Query, description = "Comma-separated domains for resource loading")
("resource_domains" = Option<String>, Query, description = "Comma-separated domains for resource loading"),
("frame_domains" = Option<String>, Query, description = "Comma-separated origins for nested iframes (frame-src)"),
("base_uri_domains" = Option<String>, Query, description = "Comma-separated allowed base URIs (base-uri)")
),
responses(
(status = 200, description = "MCP App proxy HTML page", content_type = "text/html"),
Expand All @@ -91,9 +114,16 @@ async fn mcp_app_proxy(
// Parse domains from query params
let connect_domains = parse_domains(params.connect_domains.as_ref());
let resource_domains = parse_domains(params.resource_domains.as_ref());
let frame_domains = parse_domains(params.frame_domains.as_ref());
let base_uri_domains = parse_domains(params.base_uri_domains.as_ref());

// Build the outer CSP based on declared domains
let csp = build_outer_csp(&connect_domains, &resource_domains);
let csp = build_outer_csp(
&connect_domains,
&resource_domains,
&frame_domains,
&base_uri_domains,
);

// Replace the CSP placeholder in the HTML template
let html = MCP_APP_PROXY_HTML.replace("{{OUTER_CSP}}", &csp);
Expand Down
8 changes: 8 additions & 0 deletions ui/desktop/src/components/McpApps/utils.ts
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,8 @@ export async function fetchMcpAppProxyUrl(
csp?: {
connectDomains?: string[] | null;
resourceDomains?: string[] | null;
frameDomains?: string[] | null;
baseUriDomains?: string[] | null;
} | null
): Promise<string | null> {
try {
Expand All @@ -28,6 +30,12 @@ export async function fetchMcpAppProxyUrl(
if (csp?.resourceDomains?.length) {
params.set('resource_domains', csp.resourceDomains.join(','));
}
if (csp?.frameDomains?.length) {
params.set('frame_domains', csp.frameDomains.join(','));
}
if (csp?.baseUriDomains?.length) {
params.set('base_uri_domains', csp.baseUriDomains.join(','));
}

return `${baseUrl}/mcp-app-proxy?${params.toString()}`;
} catch (error) {
Expand Down
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