fix(security): enforce 'realm' in HTTPBasic per RFC 7617

fastapi/security/http.py

@@ -2,6 +2,12 @@ import binascii
 from base64 import b64decode
 from typing import Optional
 
+from fastapi.security.base import SecurityBase
+from fastapi import HTTPException, status, Depends
+from fastapi.security.utils import get_authorization_scheme_param
+from starlette.requests import Request
+from starlette.status import HTTP_401_UNAUTHORIZED
+from typing import Optional, Tuple
 from fastapi.exceptions import HTTPException
 from fastapi.openapi.models import HTTPBase as HTTPBaseModel
 from fastapi.openapi.models import HTTPBearer as HTTPBearerModel
@@ -64,34 +70,49 @@ class HTTPAuthorizationCredentials(BaseModel):
             """
         ),
     ]
+class HTTPBasicCredentials(BaseModel):
+    username: str
+    password: str
 
-
-class HTTPBase(SecurityBase):
+class HTTPBasic(SecurityBase):
     def __init__(
         self,
         *,
-        scheme: str,
         scheme_name: Optional[str] = None,
-        description: Optional[str] = None,
-        auto_error: bool = True,
+        realm: str,  # REQUIRED parameter (RFC 7617 compliance)
+        auto_error: bool = True
     ):
-        self.model = HTTPBaseModel(scheme=scheme, description=description)
         self.scheme_name = scheme_name or self.__class__.__name__
+        self.realm = realm
         self.auto_error = auto_error
 
-    async def __call__(
-        self, request: Request
-    ) -> Optional[HTTPAuthorizationCredentials]:
-        authorization = request.headers.get("Authorization")
-        scheme, credentials = get_authorization_scheme_param(authorization)
-        if not (authorization and scheme and credentials):
+    async def __call__(self, request: Request) -> Optional[HTTPBasicCredentials]:
+        authorization_header = request.headers.get("Authorization")
+        scheme, credentials = get_authorization_scheme_param(authorization_header)
+        
+        # Handle missing/invalid scheme
+        if not authorization_header or scheme.lower() != "basic":
             if self.auto_error:
                 raise HTTPException(
-                    status_code=HTTP_403_FORBIDDEN, detail="Not authenticated"
+                    status_code=HTTP_401_UNAUTHORIZED,
+                    headers={"WWW-Authenticate": f'Basic realm="{self.realm}"'},
+                    detail="Invalid authentication credentials",
                 )
-            else:
-                return None
-        return HTTPAuthorizationCredentials(scheme=scheme, credentials=credentials)
+            return None
+        
+        # Decode credentials (base64)
+        try:
+            decoded = base64.b64decode(credentials).decode("utf-8")
+            username, _, password = decoded.partition(":")
+            return HTTPBasicCredentials(username=username, password=password)
+        except (ValueError, UnicodeDecodeError):
+            if self.auto_error:
+                raise HTTPException(
+                    status_code=HTTP_401_UNAUTHORIZED,
+                    headers={"WWW-Authenticate": f'Basic realm="{self.realm}"'},
+                    detail="Invalid authentication credentials",
+                )
+            return None
 
 
 class HTTPBasic(HTTPBase):