Update csrf.py

fix: update type annotations to pass mypy checks

fastapi/middleware/csrf.py

@@ -2,8 +2,7 @@ import functools
 import http.cookies
 import secrets
 from re import Pattern
-from typing import Any, Dict, List, Optional, Set
-
+from typing import Dict, List, Optional, Set, Any, cast, Callable, Coroutine
 from itsdangerous import BadSignature
 from itsdangerous.url_safe import URLSafeSerializer
 from starlette.datastructures import URL, MutableHeaders
@@ -134,10 +133,11 @@ class CSRFMiddleware:
     async def _get_csrf_token_form(self, request: Request) -> str:
         form = await request.form()
         csrf_token = form.get(self.cookie_name, "")
-        return csrf_token
+        return cast(str, csrf_token)
 
     def _generate_csrf_token(self) -> str:
-        return self.serializer.dumps(secrets.token_urlsafe(128))
+        token = self.serializer.dumps(secrets.token_urlsafe(128)) 
+        return cast(str, token)
 
     def _csrf_tokens_match(self, token1: str, token2: str) -> bool:
         try:
@@ -152,10 +152,9 @@ class CSRFMiddleware:
             content="CSRF token verification failed", status_code=403
         )
 
-    def _receive_with_body(self, receive, body) -> dict:
-        async def inner() -> dict:
+    def _receive_with_body(self, receive: Any, body: bytes) -> Callable[[], Coroutine[Any, Any, Dict[str, Any]]]:
+        async def inner() -> dict :
             return {"type": "http.request", "body": body, "more_body": False}
-
         return inner
 
 
@@ -171,5 +170,4 @@ def csrf_token_processor(csrf_cookie_name: str, csrf_header_name: str):
             "csrf_input": csrf_input,
             "csrf_header": csrf_header,
         }
-
     return processor