open id is said to be a protocol which uses url as username, so if a website supports openId, user only needs to input password.
you can set up your own openId registry server, or use a 3rd party openId registry, the callback URL will lead user accross identification.
open id requires the client to send request to openId registry servers, which is called IdentityServer, this is the origin of how openId works, it was first introduced by a guy.
some websites have already stopped supporting openId, like google.
openId protocol makes single point login possible, providing a universal identification server way.
oauth
oauth is another authorization protocol, which seperates into 3 main parts
there are 3 servers in oauth,
1. unauthorized request token server
2. with one, go to get authorized request token server to get authorized token, and redirect to callback url
3. with authorized token from 2, go to access token server to get access token, and access method signatures in defined timespan
原文：https://www.cnblogs.com/hualiu0/p/9567373.html