📝 Add documentation for Behind a Proxy - Proxy Forwarded Headers, using --forwarded-allow-ips="*" (#14028)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

tests/test_tutorial/test_behind_a_proxy/test_tutorial001_01.py

@@ -0,0 +1,21 @@
+from fastapi.testclient import TestClient
+
+from docs_src.behind_a_proxy.tutorial001_01 import app
+
+client = TestClient(
+    app,
+    base_url="https://example.com",
+    follow_redirects=False,
+)
+
+
+def test_redirect() -> None:
+    response = client.get("/items")
+    assert response.status_code == 307
+    assert response.headers["location"] == "https://example.com/items/"
+
+
+def test_no_redirect() -> None:
+    response = client.get("/items/")
+    assert response.status_code == 200
+    assert response.json() == ["plumbus", "portal gun"]