Added user logs for save bearer token

Purpose of those logs is to get more information
about deadlocks coming on prod when we revoke already
existing refresh tokens.

LEARNER-717

openedx/core/djangoapps/oauth_dispatch/dot_overrides.py

@@ -3,17 +3,21 @@ Classes that override default django-oauth-toolkit behavior
 """
 from __future__ import unicode_literals
 
+import logging
 from datetime import datetime
 
 from django.contrib.auth import authenticate, get_user_model
 from django.db.models.signals import pre_save
 from django.dispatch import receiver
+from pytz import utc
+
 from oauth2_provider.models import AccessToken
 from oauth2_provider.oauth2_validators import OAuth2Validator
-from pytz import utc
 
 from .models import RestrictedApplication
 
+log = logging.getLogger(__name__)
+
 
 @receiver(pre_save, sender=AccessToken)
 def on_access_token_presave(sender, instance, *args, **kwargs):  # pylint: disable=unused-argument
@@ -73,6 +77,9 @@ class EdxOAuth2Validator(OAuth2Validator):
         grant_type = request.grant_type
         user = request.user
 
+        _token_prefix = token['access_token'][:3]
+        log.info('Saving bearer token with prefix [%s] for user [%d]', _token_prefix, user.id)
+
         if grant_type == 'client_credentials':
             # Temporarily remove the grant type to avoid triggering the super method's code that removes request.user.
             request.grant_type = None
@@ -100,6 +107,8 @@ class EdxOAuth2Validator(OAuth2Validator):
 
             token['expires_in'] = expires_in
 
+        log.info('Finished bearer token with prefix [%s] for user [%d]', _token_prefix, user.id)
+
         # Restore the original request attributes
         request.grant_type = grant_type
         request.user = user

openedx/core/djangoapps/oauth_dispatch/tests/test_client_credentials.py

@@ -63,10 +63,10 @@ class ClientCredentialsTest(mixins.AccessTokenMixin, TestCase):
             'client_id': application.client_id,
             'client_secret': application.client_secret,
             'scope': ' '.join(scopes),
-            'token_type': 'jwt'
+            'token_type': 'jwt',
         }
 
-        response = self.client.post(reverse('access_token'), data)
+        response = self.client.post(reverse('access_token'), data, user=self.user)
         self.assertEqual(response.status_code, 200)
 
         content = json.loads(response.content)