[2025-03-26 spec] Implement authorization framework based on OAuth 2.1

[mikekistler]

For compliance with the 2025-03-25 Model Context Protocol spec:

• Implement support for the authorization framework based on OAuth 2.1 (PR #133)

[localden]

Tagging this for the new spec version in review: modelcontextprotocol/modelcontextprotocol#284

[halllo]

I started a prototypical implementation of the oauth endpoints required to allow the MCP Inspector to login successfully.

#258