Support 3rd party oauth authorization for MCP servers

[seanhoughton]

A desirable scenario is to have a remote MCP server protected by OAuth2 where access tokens are provided by a 3rd party. Examples include Entra ID, Auth0, or Okta. When the client (aka Roo) receives a 401 it queries the protected resource endpoint from the MCP server to discover how to log in.

Note that dynamic registration is optional in the spec, so an additional optional configuration field "clientId" could be added to the MCP server configuration for environments where dynamic registration is not supported.

Here's the spec for reference: https://modelcontextprotocol.io/specification/draft/basic/authorization