## Support semantics
This is a **candidate / unverified** Solution from the KFA Solution Factory Tier-2 gate. It is source-grounded research material, not an Outcome, and does **not** claim independent reproduction or confirmed field success.
## Cause
Transport performs one re-auth retry (isAuthRetry); second 401 is surfaced as typed SdkHttpError ClientHttpAuthentication per sdkErrors documentation.
## Steps
1. Capture the failing request URL and WWW-Authenticate headers on the 401 response.
2. Log or decode the access token claims immediately after re-auth (iss, aud, exp, scope).
3. Compare with server-side token validation rules (expected audience/resource URI, issuer, clock skew).
4. Adjust OAuth client resource parameter or server AuthInfo mapping so the server accepts the issued token.
5. Retry; expect a single auth retry leg only—persistent 401 after re-auth indicates configuration mismatch.
## Expected result
Post-re-auth request returns 200 (or non-401); CLIENT_HTTP_AUTHENTICATION no longer thrown after a successful token exchange.
## Misleading approaches
- Repeated manual OAuth without fixing audience/resource alignment.
- Assuming token refresh bugs when the server never accepted the token claims.
## Limitations
- SDK error does not include server-side rejection reason; server logs or token inspection are required.
- Exact aud/resource mismatch is deployment-specific and not encoded in the client error string.
## Unknowns
- Which specific claim failed validation for a given deployment without server-side diagnostics.
## Evidence claims
- (documented_platform_behavior) After one re-auth retry, a second HTTP 401 throws SdkHttpError with message Server returned 401 after re-authentication. — https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/7f7a94c22017e121a960e071bb50ec75e34450bd/packages/client/src/client/streamableHttp.ts
- (documented_platform_behavior) CLIENT_HTTP_AUTHENTICATION documents re-auth retry still got 401. — https://raw.githubusercontent.com/modelcontextprotocol/typescript-sdk/7f7a94c22017e121a960e071bb50ec75e34450bd/packages/core-internal/src/errors/sdkErrors.ts
Proposed approach
- Problem id
- 79504aeb-62a9-4c3f-ad52-7b94c47f77d2
- Proposed action
- After OAuth succeeds, decode the access token (or introspection result) and compare iss, aud, exp, and scopes with what the MCP server validates. Align authorization-server audience/resource (including RFC 8707 resource parameter in the authorize/token request) with the server's expected resource identifier and issuer. Fix server verifier configuration rather than adding more client retries.
- Applicability
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); @modelcontextprotocol/client v2 using Streamable HTTP or SSE transport with authProvider; OAuth completes but the second request is still 401.; affected: MCP TypeScript SDK v2 client transports; fix_status: PARTIAL
- Limitations
- State
- partial
- Text
- SDK error does not include server-side rejection reason; server logs or token inspection are required. Exact aud/resource mismatch is deployment-specific and not encoded in the client error string.
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
Needs revalidation
LOW EVIDENCE
This exact knowledge revision needs ordinary execution evidence.
Useful environment or version
- State
- partial
- Text
- support: candidate_unverified (not an Outcome; no reproduction claim); @modelcontextprotocol/cli
Reported outcomes
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