client_credentials grant type for mcp oauth

[elvis-cai]

Describe the solution you'd like
support client_credentials for app to app auth

Additional context
MCP doc mentioned https://modelcontextprotocol.io/specification/2025-03-26/basic/authorization#2-1-1-oauth-grant-types client credential grant type is also supported, just wondering if we have any plan to support it mainly for app to app auth part, thank you.

[kenany]

I'd also like to see support for this. I could work on a PR if the team is interested.

[LucaButBoring]

Interested in working on this - #982 is doing some significant refactors to OAuthClientProvider that this will need to build on top of.