Reference article:
Single sign-on: https://yq.aliyun.com/articles/636281
stateless, stateful: https://blog.csdn.net/fhkkkbfgggjk/article/details/85047461
Single sign-on: As long as there is a multiple application login module to log, the other application do not have to login.
Stateless visit: asymmetric encryption, public key save to buy a return visit to the token service can not be verified. The server does not save the user state information.
Stateful Login: server stores the user's information turntable. It will return to open session serial number, serial number verification each time.