Make class `OidcClientInitiatedLogoutSuccessHandler` extensible

oauth2/oauth2-client/src/main/java/org/springframework/security/oauth2/client/oidc/web/logout/OidcClientInitiatedLogoutSuccessHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 the original author or authors.
+ * Copyright 2002-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -45,7 +45,7 @@ import org.springframework.web.util.UriComponentsBuilder;
  * "https://openid.net/specs/openid-connect-rpinitiated-1_0.html">RP-Initiated Logout</a>
  * @see org.springframework.security.web.authentication.logout.LogoutSuccessHandler
  */
-public final class OidcClientInitiatedLogoutSuccessHandler extends SimpleUrlLogoutSuccessHandler {
+public class OidcClientInitiatedLogoutSuccessHandler extends SimpleUrlLogoutSuccessHandler {
 
 	private final ClientRegistrationRepository clientRegistrationRepository;