Add ProxyHeadersMiddleware to parse X-Forwarded-Proto header

Starlett will automatically generate redirects to add or remove trailing
slashes as appropriate. To do this it needs to know the protocol,
however. This is usually passed by the proxy in the X-Forwarded-Proto
header.

main.py

@@ -1,6 +1,11 @@
 from fastapi import FastAPI
+from uvicorn.middleware.proxy_headers import ProxyHeadersMiddleware
 app = FastAPI()
 
+app.add_middleware(
+    ProxyHeadersMiddleware, trusted_hosts=[None]
+)
+
 @app.get("/f1")
 async def f1():
     return {