Add support for Python FastAPI

[mschwager]

https://fastapi.tiangolo.com/

[ocervell]

+1 please ;)

[mschwager]

Hey @ocervell, I opened a PR with basic FastAPI support: #17. Would you mind taking a look?

FastAPI takes a different approach to authentication compared to some other Python frameworks like Flask. Flask apps typically use Python decorators to specify authn/authz information. FastAPI uses function arguments as a kind of dependency injection for authn. As a first pass, I considered authn arguments shown in these examples:

• https://fastapi.tiangolo.com/tutorial/security/first-steps/
• https://fastapi.tiangolo.com/tutorial/security/oauth2-jwt/
• https://auth0.com/blog/build-and-secure-fastapi-server-with-auth0/

Let me know if this works for you, if there are different authn arguments you think should be specified, or if you think there's a better approach altogether.