FastAPI auth check before granting access to sub-applications - jwt

Question

I am mounting a Flask app as a sub-application in my root FastAPI app, as explained in the documentation
Now I want to add an authentication layer using HTTPAuthorizationCredentials dependency, as nicely explained in this tutorial
tutorial code
How can I do that?
Preferably, I would like that any type of access attempt to my Flask sub-application goes first through a valid token authentication process implemented in my FastAPI root app. Is that possible?

Answer 1

You can use a custom WSGIMiddleware and authorize the call to flask app inside that like this:
from fastapi import FastAPI, Depends, HTTPException
from fastapi.middleware.wsgi import WSGIMiddleware
from flask import Flask, escape, request
from starlette.routing import Mount
from starlette.types import Scope, Receive, Send
flask_app = Flask(__name__)
def authenticate(authorization: str = Header()):
# Add logic to authorize user
if authorization == "VALID_TOKEN":
return
else:
raise HTTPException(status_code=401, detail="Not Authorized")
class AuthWSGIMiddleware(WSGIMiddleware):
async def __call__(self, scope: Scope, receive: Receive, send: Send) -> None:
_, authorization = next((header for header in scope['headers'] if header[0] == b'authorization'), (b'authorization', "" ))
authenticate(authorization.decode('utf-8'))
await super().__call__(scope, receive, send)
routes = [
Mount("/v1", AuthWSGIMiddleware(flask_app)),
]
# OR Optionally use this as you were doing
# The above one is preferred as per starlette docs
# app.mount("/v1", WSGIMiddleware(flask_app))
#flask_app.route("/")
def flask_main():
name = request.args.get("name", "World")
return f"Hello, {escape(name)} from Flask!"
app = FastAPI(routes=routes, dependencies=[Depends(authenticate)])
#app.get("/v2")
def read_main():
return {"message": "Hello World"}
For the tutorial you are looking at, you can replace the invoking authenticate function in my example inside AuthWSGIMiddleware->__call__() with
AuthHandler().decode_toke(authorization)