code review stuff

Author: ankit--sethi

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/authc/Authentication.java

@@ -1381,9 +1381,9 @@ public static Authentication newCloudAccessTokenAuthentication(
         Authentication.RealmRef realmRef
     ) {
         assert authResult.isAuthenticated() : "cloud access token authn result must be successful";
-        final User apiKeyUser = authResult.getValue();
+        final User user = authResult.getValue();
         return new Authentication(
-            new Subject(apiKeyUser, realmRef, TransportVersion.current(), authResult.getMetadata()),
+            new Subject(user, realmRef, TransportVersion.current(), authResult.getMetadata()),
             AuthenticationType.TOKEN
         );
     }

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/Security.java

@@ -1081,6 +1081,7 @@ Collection<Object> createComponents(
         }
 
         final List<CustomAuthenticator> customAuthenticators = getCustomAuthenticatorFromExtensions(extensionComponents);
+        components.addAll(customAuthenticators);
 
         authcService.set(
             new AuthenticationService(

x-pack/plugin/security/src/main/java/org/elasticsearch/xpack/security/authc/PluggableAuthenticatorChain.java

@@ -14,15 +14,14 @@
 import org.elasticsearch.xpack.core.security.authc.apikey.CustomAuthenticator;
 
 import java.util.List;
+import java.util.Objects;
 
 public class PluggableAuthenticatorChain implements Authenticator {
 
-    public static final PluggableAuthenticatorChain EMPTY = new PluggableAuthenticatorChain(List.of());
-
     private final List<CustomAuthenticator> customAuthenticators;
 
     public PluggableAuthenticatorChain(List<CustomAuthenticator> customAuthenticators) {
-        this.customAuthenticators = customAuthenticators;
+        this.customAuthenticators = Objects.requireNonNull(customAuthenticators);
     }
 
     @Override
@@ -56,6 +55,7 @@ public void authenticate(Context context, ActionListener<AuthenticationResult<Au
         }
         AuthenticationToken token = context.getMostRecentAuthenticationToken();
         if (token != null) {
+            //TODO switch to IteratingActionListener
             for (CustomAuthenticator customAuthenticator : customAuthenticators) {
                 if (customAuthenticator.supports(token)) {
                     customAuthenticator.authenticate(token, ActionListener.wrap(response -> {

x-pack/plugin/security/src/test/java/org/elasticsearch/xpack/security/authc/AuthenticatorChainTests.java

@@ -38,6 +38,7 @@
 import org.junit.Before;
 
 import java.io.IOException;
+import java.util.Collections;
 import java.util.List;
 
 import static org.elasticsearch.test.ActionListenerUtils.anyActionListener;
@@ -91,7 +92,7 @@ public void init() {
         oAuth2TokenAuthenticator = mock(OAuth2TokenAuthenticator.class);
         apiKeyAuthenticator = mock(ApiKeyAuthenticator.class);
         realmsAuthenticator = mock(RealmsAuthenticator.class);
-        PluggableAuthenticatorChain pluggableAuthenticatorChain = PluggableAuthenticatorChain.EMPTY;
+        PluggableAuthenticatorChain pluggableAuthenticatorChain = new PluggableAuthenticatorChain(Collections.emptyList());
 
         when(realms.getActiveRealms()).thenReturn(List.of(mock(Realm.class)));
         when(realms.getUnlicensedRealms()).thenReturn(List.of());