docs: def revoke_member(context, request):
      """Revoke member roles in the group."""
  
      mapping = request.json['mapping']
      for entry in mapping:
          user = entry['user']
          roles = entry['roles']
          username = user.get('username', None)
          userid = user.get('userid', None)
          if userid:
              u = context.get_user_by_userid(userid)
          elif username:
              u = context.get_user_by_username(username)
          else:
              u = None
          if u is None:
              raise UnprocessableError(
                  'User %s does not exists' % (userid or username))
          for rolename in roles:
              context.revoke_member_role(u.userid, rolename)
      return {'status': 'success'}