SEP-1046 and SEP-1502: Support client credentials flow as an auth extension

[D-McAdams]

This PR adds support for OAuth 2.1 Client Credentials Flow to enable machine-to-machine authentication in the MCP authorization specification. See SEP #1046

[aaronpk]

I see the file in the PR is a .mdx file. Is the idea that we'll add a static site generator to this repo too? Or will people read the extensions on github.com as the github-rendered markdown?

[D-McAdams]

I see the file in the PR is a .mdx file. Is the idea that we'll add a static site generator to this repo too? Or will people read the extensions on github.com as the github-rendered markdown?

Interesting, hadn't noticed that. It's genetic heritage from prior iterations within the core mcp repo, where all MCP specs use the .mdx suffix (not sure why). As far as I can tell, the regular .md suffix would work.

It's a fair question whether we'd also add a static site generator. Hadn't planned that work yet. For future-proofing, I could move the content under a /docs directory to be compatible with the core specs usage of Mintify, and easily enable this later.

[pcarleton]

good q on mdx... to keep it simple, I'd say let's rely on github's rendering for now

[yannj-fr]

Is this one approved?