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pythonfastapiuvicorn

FastAPI redirection for trailing slash returns non-SSL link

When we call an endpoint and a redirect occurs due to a missing trailing slash. As you can see in the image below, when a request is made to https://.../notifications, the FastAPI server responds with a redirect to http://.../notifications/

I suspect that it's an app configuration issue rather than a server configuration issue. Does anyone have an idea of how to resolve this issue?

example of redirect

Solution

  • This is because your application isn't trusting the reverse proxy's headers overriding the scheme (the X-Forwarded-Proto header that's passed when it handles a TLS request).

    There's a few ways we can fix that:

    • If you're running the application straight from uvicorn server, try using the flag --forwarded-allow-ips '*'.

    • If you're running gunicorn you can set as well the flag --forwarded-allow-ips="*".

    • In either application, you can additionally use the FORWARDED_ALLOW_IPS environment variable.

    Important: the * should be used only as a test, as it'll lead your application to trust the X-Forwarded-* headers from any source. I suggest you read uvicorn's docs and gunicorn's docs for a deeper knowledge of what to set in this flag and why.