diff --git a/zerver/lib/redis_utils.py b/zerver/lib/redis_utils.py
index af150680bb..7636b4e9c6 100644
--- a/zerver/lib/redis_utils.py
+++ b/zerver/lib/redis_utils.py
@@ -1,5 +1,5 @@
 import re
-from typing import Any, Dict, Optional
+from typing import Any, Dict, Mapping, Optional
 
 import redis
 import ujson
@@ -25,7 +25,7 @@ def get_redis_client() -> redis.StrictRedis:
                              password=settings.REDIS_PASSWORD, db=0)
 
 def put_dict_in_redis(redis_client: redis.StrictRedis, key_format: str,
-                      data_to_store: Dict[str, Any],
+                      data_to_store: Mapping[str, Any],
                       expiration_seconds: int,
                       token_length: int=64,
                       token: Optional[str]=None) -> str:
diff --git a/zerver/views/auth.py b/zerver/views/auth.py
index 4ee1b3dc98..238f8326d6 100644
--- a/zerver/views/auth.py
+++ b/zerver/views/auth.py
@@ -2,7 +2,7 @@ import logging
 import os
 import urllib
 from functools import wraps
-from typing import Any, Dict, List, Mapping, Optional, cast
+from typing import Any, Dict, List, Mapping, Optional
 
 import jwt
 from cryptography.hazmat.primitives.ciphers.aead import AESGCM
@@ -224,7 +224,7 @@ def register_remote_user(request: HttpRequest, result: ExternalAuthResult) -> Ht
     # We have verified the user controls an email address, but
     # there's no associated Zulip user account.  Consider sending
     # the request to registration.
-    kwargs = cast(Dict[str, Any], result.copy_data_dict())
+    kwargs: Dict[str, Any] = dict(result.data_dict)
     # maybe_send_to_registration doesn't take these arguments, so delete them.
     kwargs.pop('subdomain', None)
     kwargs.pop('redirect_to', None)
diff --git a/zproject/backends.py b/zproject/backends.py
index 4444300900..21c0b89a05 100644
--- a/zproject/backends.py
+++ b/zproject/backends.py
@@ -985,7 +985,7 @@ class ExternalAuthResult:
                                                                 "with login_token is disallowed.")
             self.instantiate_with_token(login_token, delete_stored_data)
         else:
-            self.data_dict = cast(ExternalAuthDataDict, {**data_dict})
+            self.data_dict = data_dict.copy()
             self.user_profile = user_profile
 
         if self.user_profile is not None:
@@ -1005,11 +1005,8 @@ class ExternalAuthResult:
             if not self.user_profile.is_mirror_dummy:
                 self.data_dict['is_signup'] = False
 
-    def copy_data_dict(self) -> ExternalAuthDataDict:
-        return self.data_dict.copy()
-
     def store_data(self) -> str:
-        key = put_dict_in_redis(redis_client, self.LOGIN_KEY_FORMAT, cast(Dict[str, Any], self.data_dict),
+        key = put_dict_in_redis(redis_client, self.LOGIN_KEY_FORMAT, self.data_dict,
                                 expiration_seconds=self.LOGIN_KEY_EXPIRATION_SECONDS,
                                 token_length=self.LOGIN_TOKEN_LENGTH)
         token = key.split(self.LOGIN_KEY_PREFIX, 1)[1]  # remove the prefix