Fix typing

Signed-off-by: Alexandre Lavigne <lavigne958@gmail.com>

gspread/auth.py

@@ -92,12 +92,12 @@ class FlowCallable(Protocol):
 
     def __call__(
         self, client_config: Mapping[str, Any], scopes: Iterable[str], port: int = 0
-    ) -> Credentials: ...
+    ) -> OAuthCredentials: ...
 
 
 def local_server_flow(
     client_config: Mapping[str, Any], scopes: Iterable[str], port: int = 0
-) -> Credentials:
+) -> OAuthCredentials:
     """Run an OAuth flow using a local server strategy.
 
     Creates an OAuth flow and runs `google_auth_oauthlib.flow.InstalledAppFlow.run_local_server <https://google-auth-oauthlib.readthedocs.io/en/latest/reference/google_auth_oauthlib.flow.html#google_auth_oauthlib.flow.InstalledAppFlow.run_local_server>`_.
@@ -113,15 +113,15 @@ def local_server_flow(
 
 def load_credentials(
     filename: Path = DEFAULT_AUTHORIZED_USER_FILENAME,
-) -> Optional[Credentials]:
+) -> Optional[OAuthCredentials]:
     if filename.exists():
         return OAuthCredentials.from_authorized_user_file(filename)
 
     return None
 
 
 def store_credentials(
-    creds: Credentials,
+    creds: OAuthCredentials,
     filename: Path = DEFAULT_AUTHORIZED_USER_FILENAME,
     strip: str = "token",
 ) -> None:
@@ -204,7 +204,7 @@ def oauth(
     authorized_user_filename = Path(authorized_user_filename)
     creds = load_credentials(filename=authorized_user_filename)
 
-    if not isinstance(creds, Credentials):
+    if not isinstance(creds, OAuthCredentials):
         with open(credentials_filename) as json_file:
             client_config = json.load(json_file)
         creds = flow(client_config=client_config, scopes=scopes)
@@ -282,13 +282,15 @@ def oauth_from_dict(
     :rtype: (:class:`gspread.client.Client`, str)
     """
 
-    creds: Credentials = None
+    creds: Optional[OAuthCredentials] = None
     if authorized_user_info is not None:
         creds = OAuthCredentials.from_authorized_user_info(authorized_user_info, scopes)
 
-    if not creds and credentials is not None:
+    if creds is None and credentials is not None:
         creds = flow(client_config=credentials, scopes=scopes)
 
+    assert creds is not None, "failed to initialize credentials"
+
     client = Client(auth=creds, http_client=http_client)
 
     # must return the creds to the user