AbstractAuthenticationToken.getName() uses UserDetails.getUsername()

Fixes gh-4877

core/src/main/java/org/springframework/security/authentication/AbstractAuthenticationToken.java

@@ -26,6 +26,7 @@ import org.springframework.security.core.GrantedAuthority;
 import org.springframework.security.core.CredentialsContainer;
 import org.springframework.security.core.AuthenticatedPrincipal;
 import org.springframework.security.core.authority.AuthorityUtils;
+import org.springframework.security.core.userdetails.UserDetails;
 
 /**
  * Base class for <code>Authentication</code> objects.
@@ -79,12 +80,14 @@ public abstract class AbstractAuthenticationToken implements Authentication,
 	}
 
 	public String getName() {
+		if (this.getPrincipal() instanceof UserDetails) {
+			return ((UserDetails) this.getPrincipal()).getUsername();
+		}
 		if (this.getPrincipal() instanceof AuthenticatedPrincipal) {
 			return ((AuthenticatedPrincipal) this.getPrincipal()).getName();
 		}
-
-		if (getPrincipal() instanceof Principal) {
-			return ((Principal) getPrincipal()).getName();
+		if (this.getPrincipal() instanceof Principal) {
+			return ((Principal) this.getPrincipal()).getName();
 		}
 
 		return (this.getPrincipal() == null) ? "" : this.getPrincipal().toString();