Merge pull request #437 from cakephp/exception

Update AuthenticationRequiredException to extend HttpException.

Author: othercorey

src/Authenticator/AuthenticationRequiredException.php

@@ -16,15 +16,15 @@
  */
 namespace Authentication\Authenticator;
 
-use RuntimeException;
+use Cake\Http\Exception\HttpException;
 
 /**
  * An exception for stateless authenticators when credentials are wrong/missing.
  *
  * Unlike `UnauthenticatedException` this class can carry authentication challenge headers.
  * and is used by stateless authenticators.
  */
-class AuthenticationRequiredException extends RuntimeException
+class AuthenticationRequiredException extends HttpException
 {
     /**
      * @var array