Make classes final where possible

Update classes that have private constructors so that they are also
declared final. In a few cases, inner-classes used private constructors
but were subclassed. These have now been changed to have package-private
constructors.

Issue gh-8945

core/src/main/java/org/springframework/security/authorization/AuthenticatedReactiveAuthorizationManager.java

@@ -34,6 +34,9 @@ public class AuthenticatedReactiveAuthorizationManager<T> implements ReactiveAut
 
 	private AuthenticationTrustResolver authTrustResolver = new AuthenticationTrustResolverImpl();
 
+	AuthenticatedReactiveAuthorizationManager() {
+	}
+
 	@Override
 	public Mono<AuthorizationDecision> check(Mono<Authentication> authentication, T object) {
 		return authentication.filter(this::isNotAnonymous).map(a -> new AuthorizationDecision(a.isAuthenticated()))
@@ -59,7 +62,4 @@ public class AuthenticatedReactiveAuthorizationManager<T> implements ReactiveAut
 		return new AuthenticatedReactiveAuthorizationManager<>();
 	}
 
-	private AuthenticatedReactiveAuthorizationManager() {
-	}
-
 }

core/src/main/java/org/springframework/security/authorization/AuthorityReactiveAuthorizationManager.java

@@ -36,7 +36,7 @@ public class AuthorityReactiveAuthorizationManager<T> implements ReactiveAuthori
 
 	private final List<String> authorities;
 
-	private AuthorityReactiveAuthorizationManager(String... authorities) {
+	AuthorityReactiveAuthorizationManager(String... authorities) {
 		this.authorities = Arrays.asList(authorities);
 	}
 

core/src/main/java/org/springframework/security/core/userdetails/User.java

@@ -334,7 +334,7 @@ public class User implements UserDetails, CredentialsContainer {
 	 * Builds the user to be added. At minimum the username, password, and authorities
 	 * should provided. The remaining attributes have reasonable defaults.
 	 */
-	public static class UserBuilder {
+	public static final class UserBuilder {
 
 		private String username;
 

core/src/test/java/org/springframework/security/PopulatedDatabase.java

@@ -26,7 +26,7 @@ import org.springframework.jdbc.core.JdbcTemplate;
  *
  * @author Ben Alex
  */
-public class PopulatedDatabase {
+public final class PopulatedDatabase {
 
 	private static TestDataSource dataSource = null;