@Secured annotation is used to specify a list of roles that are allowed to access a method or class

 OAuth2 is an authorization protocol designed to delegate access to resources on behalf of a user without sharing their credentials.

GPL License requires derivative works to be open source

A CLIENT in Keycloack  can be

@PreAuthorize: It is used to secure a method before it is executed.

 Authentication is a process used to verify user's identity..

MIT License  is the most permissive for an open source projects

Software that can be free used, modified and redistributed by anyone and everyone 

Authorization is working to determine resources, it uses user's identity and pre-defined access control rules.

Keycloack uses