Added support for raw request injection in RequestContext.

[ylassoued]

closes #195
Added support for injecting the raw request into the RequestContext.

Motivation and Context

In real-life applications, authentication may rely on request headers. In the case where the MCP server needs to act on behalf of the client to retrieve resources from a remote server or DB, thus requiring to authenticate on behalf of the client, getting the request headers is essential.
With the solution implemented in this PR, you may access the raw request from any end point as follows:

mcp = FastMCP()

@mcp.resource(uri="resource://hello")
async def get_greeting() -> str:
    ctx: Context[ServerSession, object] = mcp.get_context()
    raw_request: Request = ctx.request_context.request # Starlette Request object
    headers = raw_request.headers
    # do something with the headers

How Has This Been Tested?

Breaking Changes

The only breaking change is in typing. As a matter of fact the following generic classes have now an additional type argument RequestT (raw request type):

• class RequestContext(Generic[SessionT, LifespanContextT, RequestT])
• class Server(Generic[LifespanResultT, RequestT])

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• [x ] Documentation update

Checklist

• I have read the MCP Documentation
• [ x] My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[ylassoued]

@dsp-ant, I am not sure how the reviewing process works here. I was not able to add reviewers to this PR. Will somebody eventually be assigned as reviewer to this PR?

[georg-ort]

pls merge this it's really essential to develop professional remote mcp servers!

[ylassoued]

pls merge this it's really essential to develop professional remote mcp servers!

Thank you @georg-ort! I am hoping that someone will review it and approve it so that I may merge the PR.

[georg-ort]

Well I have to thank you @ylassoued! I'm currently using your fork in order to progress since I do need authentication context in my tool calls or our product wouldn't work.

[ylassoued]

Oh brilliant. Thank you @georg-ort for supporting this. I am glad somebody if finding it useful :-).

[emilioflc]

Thank you so much for this, @ylassoued! This looks incredibly useful across a variety of contexts. I actually ran into the exact same situation where I needed authentication context in my tool calls and came across your PR. Really appreciate you putting this together. Fingers crossed it gets reviewed and merged soon!

[ylassoued]

Thank you very much @emilioflc. My pleasure :-).