Revert "Fix HTTP Basic realm handling (RFC 7617)"

This reverts commit e8c08fc843.

fastapi/security/http.py

@@ -152,7 +152,14 @@ class HTTPBasic(HTTPBase):
                 """
             ),
         ] = None,
-        realm: Annotated[str, Doc("HTTP Basic authentication realm.")] = "fastapi",
+        realm: Annotated[
+            Optional[str],
+            Doc(
+                """
+                HTTP Basic authentication realm.
+                """
+            ),
+        ] = None,
         description: Annotated[
             Optional[str],
             Doc(
@@ -190,7 +197,9 @@ 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"}
 
     async def __call__(  # type: ignore
         self, request: Request

tests/test_security_http_base.py

@@ -1,5 +1,4 @@
-from fastapi import Depends, FastAPI, Security
+from fastapi import FastAPI, Security
-from fastapi.security import HTTPBasic
 from fastapi.security.http import HTTPAuthorizationCredentials, HTTPBase
 from fastapi.testclient import TestClient
 
@@ -54,18 +53,3 @@ 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"'