lib: Move UserBackendInterface::authenticate() to new interface Authenticatable

refs #9660

library/Icinga/Authentication/Authenticatable.php

@@ -0,0 +1,21 @@
+<?php
+/* Icinga Web 2 | (c) 2013-2015 Icinga Development Team | GPLv2+ */
+
+namespace Icinga\Authentication;
+
+use Icinga\User;
+
+interface Authenticatable
+{
+    /**
+     * Authenticate a user
+     *
+     * @param   User    $user
+     * @param   string  $password
+     *
+     * @return  bool
+     *
+     * @throws  \Icinga\Exception\AuthenticationException If authentication errors
+     */
+    public function authenticate(User $user, $password);
+}

library/Icinga/Authentication/User/UserBackendInterface.php

@@ -3,13 +3,13 @@
 
 namespace Icinga\Authentication\User;
 
-use Icinga\Exception\AuthenticationException;
+use Icinga\Authentication\Authenticatable;
 use Icinga\User;
 
 /**
  * Interface for user backends
  */
-interface UserBackendInterface
+interface UserBackendInterface extends Authenticatable
 {
     /**
      * Set this backend's name
@@ -26,16 +26,4 @@ interface UserBackendInterface
      * @return  string
      */
     public function getName();
-
-    /**
-     * Authenticate the given user
-     *
-     * @param   User        $user
-     * @param   string      $password
-     *
-     * @return  bool                        True on success, false on failure
-     *
-     * @throws  AuthenticationException     In case authentication is not possible due to an error
-     */
-    public function authenticate(User $user, $password);
 }