docs: def add_user_to_group(self, username, group):
          """Add a user to an existing group.
  
          :param username: Username that will be added to specified group.
          :type username: str
          :param group: Group that the user will be added to.
          :type group: str
  
          :return: json response from Jira server for success or a value that evaluates as False in case of failure.
          :rtype: Union[bool,Dict[str,Any]]
          """
          url = self._options['server'] + '/rest/api/latest/group/user'
          x = {'groupname': group}
          y = {'name': username}
  
          payload = json.dumps(y)
  
          r = json_loads(self._session.post(url, params=x, data=payload))
          if 'name' not in r or r['name'] != group:
              return False
          else:
              return r