Split the get_or_create_for_cognito method.

Split the method into get_user and create_for_cognito.
Spliting the method into two allows more efficient calling of the method, especially  when using access token.
The get_user method will first check whether the user exists. If exists, it will directly skip the get requests from UserInfo endpoint, and also skip the attempt for user creation, and directly return the user object.

The UserInfo endpoint will be only called during the initial registeration of the client that does not exist in User database.

Author: ckng0221

README.rst

@@ -86,3 +86,43 @@ You need to specify the Cognito domain in the ``settings.py`` file to obtain the
 .. code-block:: python
 
 	COGNITO_DOMAIN = "your-user-pool-domain"  # eg, exampledomain.auth.ap-southeast-1.amazoncognito.com
+
+To use the backend functions, at the DJANGO_USER_MODEL, could define methods as follows:
+
+.. code-block:: python
+
+    class CustomizedUserManager(UserManager):
+        def get_user(self, payload):
+            cognito_id = payload['sub']
+            try:
+                return self.get(cognito_id=cognito_id)
+            except self.model.DoesNotExist:
+                return None
+
+        def create_for_cognito(self, payload):
+            """Get any value from `payload` here
+            ipdb> pprint(payload)
+            {'aud': '159ufjrihgehb67sn373aotli7',
+            'auth_time': 1583503962,
+            'cognito:username': 'john-rambo',
+            'email': '[email protected]',
+            'email_verified': True,
+            'event_id': 'd92a99c2-c49e-4312-8a57-c0dccb84f1c3',
+            'exp': 1583507562,
+            'iat': 1583503962,
+            'iss': 'https://cognito-idp.us-west-2.amazonaws.com/us-west-2_flCJaoDig',
+            'sub': '2e4790a0-35a4-45d7-b10c-ced79be22e94',
+            'token_use': 'id'}
+            """
+            cognito_id = payload['sub']
+
+            try:
+                user = self.create(
+                    username= payload["cognito:username"] if payload.get("cognito:username") else payload["username"],
+                    cognito_id=cognito_id,
+                    email=payload['email'],
+                    is_active=True)
+            except IntegrityError:
+                user = self.get(cognito_id=cognito_id)
+
+            return user

src/django_cognito_jwt/backend.py

@@ -31,12 +31,17 @@ def authenticate(self, request):
             raise exceptions.AuthenticationFailed()
 
         USER_MODEL = self.get_user_model()
-        if settings.COGNITO_TOKEN_TYPE == "access":
-            user_info = self.get_user_info(jwt_token.decode("UTF-8"))
-            user_info = json.loads(user_info.decode("UTF-8"))
-            user = USER_MODEL.objects.get_or_create_for_cognito(user_info)
-        else:
-            user = USER_MODEL.objects.get_or_create_for_cognito(jwt_payload)
+        user = USER_MODEL.objects.get_user(jwt_payload)
+        if not user:
+            # Create new user if not exists
+            payload = jwt_payload
+            if settings.COGNITO_TOKEN_TYPE == "access":
+                user_info = self.get_user_info(jwt_token.decode("UTF-8"))
+                user_info = json.loads(user_info.decode("UTF-8"))
+                payload = user_info
+
+            user = USER_MODEL.objects.create_for_cognito(payload)
+        
         return (user, jwt_token)
 
     def get_user_model(self):