Protected Resource Metadata request failed: 404

Initial Checks

Description

In python-sdk v1.18.0, the PR #1324 introduced new scopes selection and step-up authorization. but in the step 1

else:
raise OAuthFlowError(f"Protected Resource Metadata request failed: {response.status_code}")

It raise an error if the oauth-protected-resource url is not found on server. this cause issue for old mcp server that does not support it yet. for example https://mcp.linear.app/sse or https://mcp.atlassian.com/v1/sse

Since we still allows discover fallback url in step 4. I suggest we should remove this exception and let the flow fall through.

Example Code

Python & MCP Python SDK