获取token LoginHandler can be used by clients to get a jwt token. Payload needs to be json in the form of {"username": "USERNAME", "password": "PASSWORD"}. Reply will be of the form {"token": "TOKEN"}. dev mode:It should be noted that all fields cannot be empty, and a value of 0 can be passed in addition to the account password 注意:开发模式:需要注意全部字段不能为空,账号密码外可以传入0值