Location returned by redirect_slashes should be relative instead of absolute

[rijenkii]

I have a following setup:

Browser --(https)--> Nginx --(http)--> FastAPI/Starlette

When a browser accidentally calls an endpoint without an ending slash, Starlette responds with a 307 with Location: http://example.org/api/endpoint/, which browser rightfully rejects because of mixed content blocking.

If Starlette responded with Location: /api/endpoint/ instead, browser would then just slap that relative location to the current host.

Django does it like that, but they respond with 301s:

> GET /api/endpoint HTTP/1.1

< HTTP/1.1 301 Moved Permanently
< location: /api/endpoint/