CakePHP 2.x User model for use with Role ACL

User.php

<?php
App::uses('AppModel', 'Model');
App::uses('SimplePasswordHasher', 'Controller/Component/Auth');

class User extends AppModel {

  public $actsAs = [
    'Acl' => ['type' => 'requester']
  ];

  public $belongsTo = [
    'Role' => [
      'className'  => 'Role',
      'foreignKey' => 'role_id'
    ]
  ];

  public $validate = [
    'username' => [
      'notempty' => [
        'rule'       => ['notempty'],
        'message'    => 'You must include a username',
        'allowEmpty' => false,
        'on'         => 'create'
      ]
    ],
    'role_id' => [
      'numeric' => [
        'rule'       => ['numeric'],
        'message'    => 'No role specified',
        'allowEmpty' => false
      ]
    ],
    'email' => [
      'email' => [
        'rule'       => ['email'],
        'message'    => 'You must include an email address',
        'allowEmpty' => false,
        'on'         => 'create'
      ]
    ],
    'first_name' => [
      'notempty' => [
        'rule'       => ['notempty'],
        'message'    => 'You must provide a first name',
        'allowEmpty' => false,
        'on'         => 'create'
      ]
    ],
    'last_name' => [
      'notempty' => [
        'rule'       => ['notempty'],
        'message'    => 'You must provide a last name',
        'allowEmpty' => false,
        'on'         => 'create'
      ]
    ]
  ];

  public function parentNode() {

    if (!$this->id && empty($this->data)) {
      return null;
    }

    if (isset($this->data[$this->alias]['role_id'])) {
      $role_id = $this->data[$this->alias]['role_id'];
    } else {
      $role_id = $this->field('role_id');
    }

    if (!$role_id) {
      return null;
    } else {
      return ['Role' => ['id' => $role_id]];
    }
  }

  /**
   * implement Role-only ACL: skip checks on User AROs
   *
   * @param  array  User data
   * @return  array
   * @access  public 
   */
  public function bindNode($user) {
    return [
      'model'       => 'Role',
      'foreign_key' => $user[$this->alias]['role_id']
    ];
  }


  /**
   * Hash password before save if present in data
   * 
   * @param  array  $options save options
   * @return boolean         true to continue, false to cancel save
   */
  public function beforeSave($options = []) {
    parent::beforeSave($options);

    // do not use isset() here!!
    if (!empty($this->data[$this->alias]['password'])) {

      $PasswordHasher = new SimplePasswordHasher( ['hashType' => 'sha256'] );
      $this->data[$this->alias]['password'] = $PasswordHasher->hash($this->data[$this->alias]['password']);
    }
    
    return true;
  }

}