old_contents: from django.db import models
  from django.conf import settings
  
  
  class AppToAppPermission(models.Model):
      requester = models.ForeignKey(settings.OAUTH2_PROVIDER_APPLICATION_MODEL,
                                    db_index=True, related_name='+')
      target = models.ForeignKey(settings.OAUTH2_PROVIDER_APPLICATION_MODEL,
                                 db_index=True, related_name='+')
  
new_contents: from django.db import models
  from django.conf import settings
  
  
  class AppToAppPermission(models.Model):
      requester = models.ForeignKey(settings.OAUTH2_PROVIDER_APPLICATION_MODEL,
                                    db_index=True, related_name='+')
      target = models.ForeignKey(settings.OAUTH2_PROVIDER_APPLICATION_MODEL,
                                 db_index=True, related_name='+')
  
      def __str__(self):
          return "%s -> %s" % (self.requester, self.target)
  
subject: Add __str__ method to AppToAppPermission