'Add a user to an existing group.
:param username: Username that will be added to specified group.
:param group: Group that the user will be added to.
:return: json response from Jira server for success or a value that evaluates as False in case of failure.'

def add_user_to_group(self, username, group):

    url = (self._options[u'server'] + u'/rest/api/latest/group/user')
    x = {u'groupname': group}
    y = {u'name': username}
    payload = json.dumps(y)
    r = json_loads(self._session.post(url, params=x, data=payload))
    if ((u'name' not in r) or (r[u'name'] != group)):
        return False
    else:
        return r
