Update What's New for 5.6

docs/modules/ROOT/pages/whats-new.adoc

@@ -43,6 +43,10 @@ Below are the highlights of the release.
 [[whats-new-webflux]]
 == WebFlux
 
+* OAuth 2.0 Login
+
+** Improved xref:reactive/oauth2/login/index.adoc[Reactive OAuth 2.0 Login Documentation]
+
 * OAuth 2.0 Client
 
 ** Improved https://github.com/spring-projects/spring-security/pull/9791[Client Credentials encoding]
@@ -50,4 +54,4 @@ Below are the highlights of the release.
 ** Added https://github.com/spring-projects/spring-security/pull/10269[custom response parsing] for Access Token Requests
 ** Added https://github.com/spring-projects/spring-security/pull/10327[jwt-bearer Grant Type support] for Access Token Requests
 ** Added https://github.com/spring-projects/spring-security/pull/10336[JWT Client Authentication support] for Access Token Requests
-** Improved https://github.com/spring-projects/spring-security/pull/10373[Reactive OAuth 2.0 Client Documentation]
+** Improved xref:reactive/oauth2/client/index.adoc[Reactive OAuth 2.0 Client Documentation]