CognitoIdentity: get_credentials_for_identity() should have Expiratio…

…n as number. (getmoto#7059)

moto/cognitoidentity/models.py

@@ -5,7 +5,7 @@
 from collections import OrderedDict
 from typing import Any, Dict, List, Optional
 from moto.core import BaseBackend, BackendDict, BaseModel
-from moto.core.utils import iso_8601_datetime_with_milliseconds, utcnow
+from moto.core.utils import utcnow
 from .exceptions import InvalidNameException, ResourceNotFoundError
 from .utils import get_random_identity_id
 
@@ -139,12 +139,11 @@ def get_credentials_for_identity(self, identity_id: str) -> str:
         duration = 90
         now = utcnow()
         expiration = now + datetime.timedelta(seconds=duration)
-        expiration_str = str(iso_8601_datetime_with_milliseconds(expiration))
         return json.dumps(
             {
                 "Credentials": {
                     "AccessKeyId": "TESTACCESSKEY12345",
-                    "Expiration": expiration_str,
+                    "Expiration": expiration.timestamp(),
                     "SecretKey": "ABCSECRETKEY",
                     "SessionToken": "ABC12345",
                 },