[Answer]-Not able to expose 'auth_user_groups' table in Tastypie UserResource

As stated by the tastypie docs :

ModelResource subclass will introspect all non-relational fields

So you must add the groups field to your UserResource :

class UserResource(ModelResource):
  groups = fields.ManyToManyField(GroupResource, 'groups', null=True, full=True)

  class Meta:
     [...]