Populate the subject property in the AccesToken in get_access_token()

[piaudonn]

Enhancement

Problem

get_access_token() returns an AccessToken object which does not contain a subject property.

fastmcp/fastmcp_slim/fastmcp/server/dependencies.py

Lines 519 to 527 in 0f4f78c

	return AccessToken(
	token=access_token_as_dict["token"],
	client_id=access_token_as_dict["client_id"],
	scopes=access_token_as_dict["scopes"],
	# Optional fields
	expires_at=access_token_as_dict.get("expires_at"),
	resource=access_token_as_dict.get("resource"),
	claims=access_token_as_dict.get("claims") or {},
	)

This makes early logging for authentication incomplete (and in my case made my troubleshooting of auth issue quite tedious).

Reproduction

Just invoke get_access_token() and print the output. It will return an AccessToken with the property subject set to None despite having a "sub" in the actual access token returned by the authorization server.

Expected

As per RFC9068 - RFC JSON Web Token (JWT) Profile for OAuth 2.0 Access Tokens the "sub" claim is REQUIRED and must be provided by the authorization server. I suggest subject should be set with subject=access_token_as_dict["subject"],.

[piaudonn]

What I have is incomplete of a fix as suggested by the codex review... The TokenVerifier would also need to return it. Well, I need your help :) It work on my code, but that's because I create a custom TokenVerifier.