Fix typing of samesite paramater in CookieTransport

fastapi_users/authentication/transport/cookie.py

@@ -1,5 +1,11 @@
+import sys
 from typing import Any, Optional
 
+if sys.version_info < (3, 8):
+    from typing_extensions import Literal  # pragma: no cover
+else:
+    from typing import Literal  # pragma: no cover
+
 from fastapi import Response, status
 from fastapi.security import APIKeyCookie
 
@@ -18,7 +24,7 @@ class CookieTransport(Transport):
         cookie_domain: Optional[str] = None,
         cookie_secure: bool = True,
         cookie_httponly: bool = True,
-        cookie_samesite: str = "lax",
+        cookie_samesite: Literal["lax", "strict", "none"] = "lax",
     ):
         self.cookie_name = cookie_name
         self.cookie_max_age = cookie_max_age