Fix HTTP Basic realm handling (RFC 7617)

fastapi/security/http.py

@@ -152,14 +152,7 @@ class HTTPBasic(HTTPBase):
                 """
             ),
         ] = None,
-        realm: Annotated[
-            Optional[str],
-            Doc(
-                """
-                HTTP Basic authentication realm.
-                """
-            ),
-        ] = None,
+        realm: Annotated[str, Doc("HTTP Basic authentication realm.")] = "fastapi",
         description: Annotated[
             Optional[str],
             Doc(
@@ -197,9 +190,7 @@ class HTTPBasic(HTTPBase):
         self.auto_error = auto_error
 
     def make_authenticate_headers(self) -> dict[str, str]:
-        if self.realm:
-            return {"WWW-Authenticate": f'Basic realm="{self.realm}"'}
-        return {"WWW-Authenticate": "Basic"}
+        return {"WWW-Authenticate": f'Basic realm="{self.realm}"'}
 
     async def __call__(  # type: ignore
         self, request: Request

tests/test_security_http_base.py

@@ -1,6 +1,7 @@
-from fastapi import FastAPI, Security
+from fastapi import FastAPI, Security, Depends
 from fastapi.security.http import HTTPAuthorizationCredentials, HTTPBase
 from fastapi.testclient import TestClient
+from fastapi.security import HTTPBasic
 
 app = FastAPI()
 
@@ -53,3 +54,18 @@ def test_openapi_schema():
             "securitySchemes": {"HTTPBase": {"type": "http", "scheme": "Other"}}
         },
     }
+
+def test_http_basic_includes_realm():
+    app = FastAPI()
+    security = HTTPBasic(realm="MyRealm")
+
+    @app.get("/")
+    def read_root(credentials=Depends(security)):
+        return {"ok": True}
+
+    client = TestClient(app)
+    response = client.get("/")
+
+    assert response.status_code == 401
+    assert response.headers["WWW-Authenticate"] == 'Basic realm="MyRealm"'
+