Fix OAuth metadata validation for compliant servers #778
+2
−2
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
The OAuthMetadata validation was too restrictive, rejecting valid OAuth 2.0 server configurations that advertise additional authentication methods beyond the minimum required set. Changes: - Allow 'client_secret_basic' in token_endpoint_auth_methods_supported - Allow 'plain' in code_challenge_methods_supported This fixes compatibility with MCP servers like Asana (mcp.asana.com) that advertise support for multiple OAuth authentication methods as allowed by the OAuth 2.0 specification and MCP specification. The MCP specification does not restrict which authentication methods servers can support, only requiring that PKCE is used. These changes ensure the client can connect to any compliant MCP server regardless of which optional authentication methods they also support.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Problem
The
OAuthMetadatavalidation insrc/mcp/shared/auth.pywas overly restrictive, rejecting valid OAuth 2.0 server configurations that advertise additional authentication methods beyond the minimum required set.This caused connection failures with compliant MCP servers like Asana (
mcp.asana.com) that support multiple OAuth authentication methods as allowed by the specifications.Root Cause
The server returns:
token_endpoint_auth_methods_supported:["client_secret_basic","client_secret_post","none"]code_challenge_methods_supported:["plain","S256"]But the client validation only accepted:
token_endpoint_auth_methods_supported:["none", "client_secret_post"]code_challenge_methods_supported:["S256"]Solution
Expanded the validation to accept additional methods:
client_secret_basictotoken_endpoint_auth_methods_supportedplaintocode_challenge_methods_supportedCompliance Verification
✅ MCP Specification Compliant: The MCP authorization specification does not restrict which authentication methods servers can support - it only requires PKCE support.
✅ OAuth 2.0 Compliant: These are standard OAuth 2.0 authentication methods defined in relevant RFCs.
Testing
https://mcp.asana.com/sseImpact
This fix enables the MCP Python SDK to work with any compliant MCP server regardless of which optional OAuth authentication methods they advertise support for.