Set user on the X-Ray segment from ASGI scope or framework's request

[garyd203]

If the X-Ray middleware is called after any authentication/session middleware, then the ASGI scope will probably contain some sort of reference to the authenticated user, which we can use to automatically set the user field on the Segment.

Here's some examples of how different web frameworks set the user:

• aiohttp has no built-in user concept.
• aiohttp-jwt will store the decoded JWT in a configurable key on the request (default payload)
• FastAPI does what Starlette does
• Piccolo extends Starlette's AuthenticationMiddleware (see below), and also adds a secret_token_user key to the scope.
• Starlette's builtin AuthenticationMiddleware adds a user key to the scope and a user attribute on the request. So any of scope["user"].display_name or request.user.display_name is correct (but also check user.is_authenticated)