Fix: Add realm to Basic Auth WWW-Authenticate header (RFC 7617 compliance)

fastapi/security/http.py

@@ -189,10 +189,10 @@ class HTTPBasic(HTTPBase):
     ) -> Optional[HTTPBasicCredentials]:
         authorization = request.headers.get("Authorization")
         scheme, param = get_authorization_scheme_param(authorization)
-        if self.realm:
-            unauthorized_headers = {"WWW-Authenticate": f'Basic realm="{self.realm}"'}
-        else:
-            unauthorized_headers = {"WWW-Authenticate": "Basic"}
+        # Always include a realm as required by RFC 7617.
+        realm_value = self.realm or "fastapi"
+        unauthorized_headers = {"WWW-Authenticate": f'Basic realm="{realm_value}"'}
+
         if not authorization or scheme.lower() != "basic":
             if self.auto_error:
                 raise HTTPException(

tests/test_httpbasic_realm.py

@@ -0,0 +1,29 @@
+from fastapi import Depends, FastAPI
+from fastapi.security import HTTPBasic
+from fastapi.testclient import TestClient
+
+def test_default_realm_is_included():
+    app = FastAPI()
+    security = HTTPBasic()
+
+    @app.get("/protected")
+    def protected(_: str = Depends(security)):
+        return {"ok": True}
+
+    client = TestClient(app)
+    response = client.get("/protected")
+    assert response.status_code == 401
+    assert response.headers["www-authenticate"] == 'Basic realm="fastapi"'
+
+def test_custom_realm_is_respected():
+    app = FastAPI()
+    security = HTTPBasic(realm="custom")
+
+    @app.get("/protected")
+    def protected(_: str = Depends(security)):
+        return {"ok": True}
+
+    client = TestClient(app)
+    response = client.get("/protected")
+    assert response.status_code == 401
+    assert response.headers["www-authenticate"] == 'Basic realm="custom"'

tests/test_security_http_basic_optional.py

@@ -37,7 +37,7 @@ def test_security_http_basic_invalid_credentials():
         "/users/me", headers={"Authorization": "Basic notabase64token"}
     )
     assert response.status_code == 401, response.text
-    assert response.headers["WWW-Authenticate"] == "Basic"
+    assert response.headers["WWW-Authenticate"] == 'Basic realm="fastapi"'
     assert response.json() == {"detail": "Invalid authentication credentials"}
 
 
@@ -46,7 +46,7 @@ def test_security_http_basic_non_basic_credentials():
     auth_header = f"Basic {payload}"
     response = client.get("/users/me", headers={"Authorization": auth_header})
     assert response.status_code == 401, response.text
-    assert response.headers["WWW-Authenticate"] == "Basic"
+    assert response.headers["WWW-Authenticate"] == 'Basic realm="fastapi"'
     assert response.json() == {"detail": "Invalid authentication credentials"}
 
 

tests/test_tutorial/test_security/test_tutorial006.py

@@ -32,7 +32,7 @@ def test_security_http_basic_no_credentials(client: TestClient):
     response = client.get("/users/me")
     assert response.json() == {"detail": "Not authenticated"}
     assert response.status_code == 401, response.text
-    assert response.headers["WWW-Authenticate"] == "Basic"
+    assert response.headers["WWW-Authenticate"] == 'Basic realm="fastapi"'
 
 
 def test_security_http_basic_invalid_credentials(client: TestClient):
@@ -40,7 +40,7 @@ def test_security_http_basic_invalid_credentials(client: TestClient):
         "/users/me", headers={"Authorization": "Basic notabase64token"}
     )
     assert response.status_code == 401, response.text
-    assert response.headers["WWW-Authenticate"] == "Basic"
+    assert response.headers["WWW-Authenticate"] == 'Basic realm="fastapi"'
     assert response.json() == {"detail": "Invalid authentication credentials"}
 
 
@@ -49,7 +49,7 @@ def test_security_http_basic_non_basic_credentials(client: TestClient):
     auth_header = f"Basic {payload}"
     response = client.get("/users/me", headers={"Authorization": auth_header})
     assert response.status_code == 401, response.text
-    assert response.headers["WWW-Authenticate"] == "Basic"
+    assert response.headers["WWW-Authenticate"] == 'Basic realm="fastapi"'
     assert response.json() == {"detail": "Invalid authentication credentials"}