Provide mechanism to map UserDetails to GrantedAuthority

If spring-security support such extension:

@FunctionalInterface
public interface UserAuthorityMapper {

	Collection<? extends GrantedAuthority> mapAuthorities(UserDetails user);

}

@FunctionalInterface
public interface UserRoleMapper extends UserAuthorityMapper {

	Collection<String> mapRoles(UserDetails user);

	@Override
	default Collection<? extends GrantedAuthority> mapAuthorities(UserDetails user) {
		return mapRoles(user).stream().map(SimpleGrantedAuthority::new).collect(Collectors.toList());
	}

}

and have a built-in implementation:

@Component
public class UsernameAndTypeRoleMapper implements UserRoleMapper {

	@Override
	public Collection<String> mapRoles(UserDetails user) {
		return List.of(mapUsername(user), mapUserType(user));
	}

	protected String mapUsername(UserDetails user) {
		return "USERNAME(" + user.getUsername() + ")";
	}

	protected String mapUserType(UserDetails user) {
		Class<?> c = ReflectionUtils.getEntityClass(user);
		String name = c.getSimpleName();
		if (!StringUtils.hasLength(name)) {
			name = c.getSuperclass().getSimpleName();
		}
		return name.toUpperCase();
	}

}

Then every user will have an unique username role and type role, take User admin = new User("admin") for example, role USERNAME(admin) and USER will be added to its authorities.

I would like to submit a PR if the team decide to accept this feature request.

Review the proposed UserAuthorityMapper, UserRoleMapper, and UsernameAndTypeRoleMapper interfaces in the issue, then trace how Spring Security currently maps UserDetails to GrantedAuthority. No repository files or tests are identified, so first locate the relevant authority-mapping entry points and existing tests; done means an accepted design and verified username and user-type authorities without changing the requested behavior.