ProviderManager is the mostly used implementation of AuthenticationManager.

.

AuthenticationManager is the API that describes that how Spring Security's filters perform authentication.

Method-Level security in Spring Security is done by using @PreAuthorize and @PostAuthorize annotations

UserDetails object represents the authenticated user, and it contains all the details such as the username, password, authorities (roles) etc

UserDetailsService has a single method called loadUserByUsername()

UserDetailsService  is responsible for retrieving user information from a backend data source, such as a database

OAuth2 provides authorization flows and not the authentication

No need to store user sessions on the server; JWT contains all necessary data.

.

Authorization  checks credentials like username and password provided by user against stored credentials.

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