Authentication subclasses Principal, so it's directly usable by classes that want a Principal. No implementations need to change if they subclass AbstractAuthenticationToken, as it implements the one and only method required by Principal.

core/src/main/java/org/acegisecurity/Authentication.java

@@ -15,6 +15,9 @@
 
 package net.sf.acegisecurity;
 
+import java.security.Principal;
+
+
 /**
  * Represents an authentication request.
  * 
@@ -30,7 +33,7 @@ package net.sf.acegisecurity;
  * @author Ben Alex
  * @version $Id$
  */
-public interface Authentication {
+public interface Authentication extends Principal {
     //~ Methods ================================================================
 
     public void setAuthenticated(boolean isAuthenticated);

core/src/main/java/org/acegisecurity/providers/AbstractAuthenticationToken.java

@@ -27,6 +27,10 @@ import net.sf.acegisecurity.Authentication;
 public abstract class AbstractAuthenticationToken implements Authentication {
     //~ Methods ================================================================
 
+    public String getName() {
+        return this.getPrincipal().toString();
+    }
+
     public boolean equals(Object obj) {
         if (obj instanceof AbstractAuthenticationToken) {
             AbstractAuthenticationToken test = (AbstractAuthenticationToken) obj;

core/src/test/java/org/acegisecurity/providers/AbstractAuthenticationTokenTests.java

@@ -55,6 +55,7 @@ public class AbstractAuthenticationTokenTests extends TestCase {
                         "ROLE_TWO")});
         assertEquals("Test", token.getPrincipal());
         assertEquals("Password", token.getCredentials());
+        assertEquals("Test", token.getName());
     }
 
     public void testObjectsEquals() throws Exception {