SimpUser exposes Principal

Closes gh-25191

spring-messaging/src/main/java/org/springframework/messaging/simp/user/MultiServerUserRegistry.java

@@ -18,6 +18,7 @@ package org.springframework.messaging.simp.user;
 
 import java.net.InetAddress;
 import java.net.UnknownHostException;
+import java.security.Principal;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -310,6 +311,12 @@ public class MultiServerUserRegistry implements SimpUserRegistry, SmartApplicati
 			return this.name;
 		}
 
+		@Nullable
+		@Override
+		public Principal getPrincipal() {
+			return null;
+		}
+
 		@Override
 		public boolean hasSessions() {
 			if (this.sessionLookup != null) {

spring-messaging/src/main/java/org/springframework/messaging/simp/user/SimpUser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.messaging.simp.user;
 
+import java.security.Principal;
 import java.util.Set;
 
 import org.springframework.lang.Nullable;
@@ -33,6 +34,15 @@ public interface SimpUser {
 	 */
 	String getName();
 
+	/**
+	 * Return the user associated with the session, if available. Typically, the
+	 * user information is available unless the user is connected to a different
+	 * server in a multi-server user registry scenario.
+	 * @since 5.3
+	 */
+	@Nullable
+	Principal getPrincipal();
+
 	/**
 	 * Whether the user has any sessions.
 	 */

spring-messaging/src/test/java/org/springframework/messaging/simp/user/TestSimpUser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -16,11 +16,14 @@
 
 package org.springframework.messaging.simp.user;
 
+import java.security.Principal;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 
+import org.springframework.lang.Nullable;
+
 /**
  * @author Rossen Stoyanchev
  */
@@ -41,6 +44,12 @@ public class TestSimpUser implements SimpUser {
 		return name;
 	}
 
+	@Nullable
+	@Override
+	public Principal getPrincipal() {
+		return null;
+	}
+
 	@Override
 	public Set<SimpSession> getSessions() {
 		return new HashSet<>(this.sessions.values());