Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

Authentication providers such as Keycloak support an OAuth2 extension called JARM (JWT Secured Authorization Response Mode) which defines new values for the response_modes_supported member of the OAuthMetadata response. See https://openid.net/specs/oauth-v2-jarm.html#name-response-encoding for details.

The pydantic model for OAuthMetadata only allows certain values in the response, which causes the model construction and remainder of the auth flow to fail.

I would propose relaxing the validation such that response_modes_supported is simply a list[str].

Example Code

Python & MCP Python SDK

python 3.13
mcp v1.12.3