How to implement OAuth2 server on your web server?

Question

Java

There is a web server written in Java with the ability to authorize, you need to add to it the ability to authorize other sites without using additional ports and web servers.
I would like to have a library that accepts a query constructor for input.

Answer 1

There are several libraries ranging from apache shiro to scribejava. You can announce the entire list - https://oauth.net/code/java/
And how to attach a specific lib to your application - I won’t say, you need to look at the code. But I recommend scribejava or Apache Shiro . the latter is more complicated, as it works through Pac4j

Answer 2

we take any Identity Server (for example, Keycloak), or SaaS (Auth0) and transfer the existing users of the system there. Then we set up other types of logins and integrate them into the new version using OpenId + JWT, for example. PROFIT