Regression in OAuth metadata discovery in mcp-inspector 0.21.x against authorization servers that reject Content-Type: application/json

[ensonik]

Inspector Version

0.21.1

Summary

When using mcp-inspector 0.21.1 against our MCP server, the OAuth flow fails while fetching authorization server metadata from /.well-known/oauth-authorization-server.

Our authorization server responds with 415 Unsupported Media Type when that request includes Content-Type: application/json.

This flow worked for us with mcp-inspector 0.19.0.

Regression range

• Works: mcp-inspector 0.19.0
• Fails: mcp-inspector 0.21.1
• I did not test 0.20.0

Steps to reproduce

1. Run mcp-inspector 0.21.1
2. Connect to an MCP server whose OAuth flow uses an authorization server that rejects GET /.well-known/oauth-authorization-server when Content-Type: application/json is present
3. Start the OAuth flow

Actual behavior

• Inspector requests /.well-known/oauth-authorization-server
• The authorization server returns 415
• OAuth metadata discovery fails and the OAuth flow cannot continue

Expected behavior

• mcp-inspector 0.21.x should remain compatible with setups that worked with 0.19.0
• If the current request shape is intentional, it would still help to know what changed between 0.19.0 and 0.21.x and whether there is a compatibility workaround