`auth` specification in `ClientSessionGroup`

[erwang01]

Description

It would be nice for the ClientSessionGroup to be OAuth compatible by allowing us to specify the OAuth httpx.Auth provider when passing in the ServerParameters rather than passing the bearer tokens manually via the headers field. This will allow us to do the OAuth token exchange flow straight from the ClientSessionGroup.

References

Here is the singleton ClientSession example of an OAuth flow: https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/clients/simple-auth-client/mcp_simple_auth_client/main.py

It would be nice to have an example of a ClientSessionGroup using that same flow.

[the-ayyi]

@maxisbey Let me know if anyone is working on this. Otherwise, I will take this.

[IT-HONGREAT]

Hi @maxisbey !!
I've implemented this by adding an auth: httpx.Auth | None field to both SseServerParameters & StreamableHttpParameters,which gets passed through to the underlying sse_client() and create_mcp_http_client() calls. Will open a PR shortly.

[musi22]

Hi! I’m interested in implementing this. I traced the ClientSessionGroup connection path and propose adding optional httpx2.Auth support directly on SseServerParameters and StreamableHttpParameters, propagating it into sse_client and create_mcp_http_client. Existing header behavior remains 100% backward compatible, and authentication applies cleanly only to the relevant HTTP transports.

I have implemented this with 100% test coverage, serialization safety (ConfigDict(arbitrary_types_allowed=True, exclude=True)), per-server auth isolation, and updated documentation in session-groups.md.

Would you like me to open the PR for review?