fix(mcp): require MCP_JWT_AUDIENCE when MCP JWT auth is enabled#41292
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fix(mcp): require MCP_JWT_AUDIENCE when MCP JWT auth is enabled#41292rusackas wants to merge 1 commit into
rusackas wants to merge 1 commit into
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When MCP JWT auth is enabled (MCP_AUTH_ENABLED=True) but no audience is configured, the verifier was constructed with audience validation skipped, so any otherwise-valid same-issuer token was accepted regardless of which service it was minted for. Require MCP_JWT_AUDIENCE to be set when JWT auth is enabled. The default auth factory now raises a dedicated MCPAuthConfigError, and the server bootstrap re-raises it so the MCP service fails fast at startup with a clear message instead of silently coming up in a permissive (or unauthenticated) state. API-key-only deployments are unaffected. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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## master #41292 +/- ##
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SUMMARY
When the MCP service has JWT auth enabled (
MCP_AUTH_ENABLED=True), the audience claim was only validated ifMCP_JWT_AUDIENCEhappened to be set. With it unset, the verifier was built with audience validation skipped, so any otherwise-valid token from the same issuer was accepted regardless of which service it was minted for.This makes audience configuration a required precondition for MCP JWT auth so tokens are correctly bound to this service:
create_default_mcp_auth_factory) now raises a dedicatedMCPAuthConfigErrorwhenMCP_AUTH_ENABLEDis true butMCP_JWT_AUDIENCEis unset._create_auth_provider) re-raises that error rather than swallowing it. This matters because a swallowed build error returns aNoneprovider, and the start path treatsauth_provider is Noneas "auth disabled" — i.e. the service would otherwise come up unauthenticated. Failing closed makes the misconfiguration a fast, explicit startup error instead.The check is placed at the config/bootstrap layer so it covers both verifier variants (
MCPJWTVerifierandDetailedJWTVerifier) uniformly.BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF
N/A — backend configuration behavior.
TESTING INSTRUCTIONS
Unit tests added in
tests/unit_tests/mcp_service/test_mcp_config.pyandtests/unit_tests/mcp_service/test_mcp_server.py:MCP_AUTH_ENABLED=TruewithoutMCP_JWT_AUDIENCEraisesMCPAuthConfigError._create_auth_providerpropagatesMCPAuthConfigErrorinstead of returningNone.Manual: start the MCP service with
MCP_AUTH_ENABLED=TrueandMCP_JWT_AUDIENCEunset → startup fails with a clear message. SetMCP_JWT_AUDIENCE→ starts normally.ADDITIONAL INFORMATION