fix: work around rmcp OAuth discovery bug for remote MCP servers#8583
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fix: work around rmcp OAuth discovery bug for remote MCP servers#8583
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…vers When a remote MCP server returns HTTP 200 with non-JSON content at its base URL, rmcp's resource metadata discovery fatally errors instead of falling through to .well-known/oauth-authorization-server discovery. This prevents the OAuth browser flow from ever opening. Add a fallback in oauth_flow that catches the discovery failure and retries by fetching .well-known/oauth-authorization-server directly. Also log the actual error when oauth_flow fails instead of silently swallowing it. Upstream fix: modelcontextprotocol/rust-sdk#810
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Follow the MCP spec discovery flow in the fallback path: 1. Fetch Protected Resource Metadata from .well-known/oauth-protected-resource (path-specific then root, per RFC 9728) 2. Extract the authorization server URL from authorization_servers 3. Discover Authorization Server Metadata from that URL (trying RFC 8414 and OpenID Connect well-known endpoints) This correctly handles cases where the authorization server is on a different host from the MCP server, and path-based deployments.
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Summary
Fixes the OAuth flow never opening a browser for remote MCP servers that require authentication (e.g. Attio). The root cause is an rmcp bug where resource metadata discovery fails fatally when the MCP server returns HTTP 200 with non-JSON content at its base URL, preventing fallback to
.well-known/oauth-authorization-serverdiscovery.This PR adds a fallback in
oauth_flowthat catches the discovery failure and retries by fetching.well-known/oauth-authorization-serverdirectly, using rmcp's publicAuthorizationManager/AuthorizationSessionAPIs. It also logs the actual error whenoauth_flowfails, instead of silently swallowing it.Testing
Manual testing with the Attio MCP server (
https://mcp.attio.com/mcp).Related Issues
Relates to #8453
Upstream PR: modelcontextprotocol/rust-sdk#810