My Kohana 3.3 Security class with CSRF Validation helper method

Security.php

<?php defined('SYSPATH') or die('No direct script access.');

class Security extends Kohana_Security {
	
	protected static $_logout_token_name = 'logout_token_key';

	public static $csrf_field = 'token';

	/**
	 * Creates a validation object to check if the field specified 
	 * is a valid CSRF token inside of Requests POST / GET
	 * 
	 * If no field is passed, Security::$csrf_field will be used as the name
	 * 
	 * @param  Request $request
	 * @param  string  $field (optional)
	 * @return Validation
	 */
	public static function csrf_validation(Request $request, $field = NULL)
	{
		if ($field === NULL)
		{
			$field = Security::$csrf_field;
		}
		
		// Decide if POST or GET should be checked...
		$data = ($request->method() === Request::POST) ? $request->post() : $request->query();
		
		// Return the newly created Validation object
		return Validation::factory($data)
			->rule($field, 'not_empty')
			->rule($field, 'Security::check');
	}
	
	/**
	 * Returns the token required for logout (for GET-based CSRF prevention)
	 * 
	 * @return string token
	 */
	public static function logout_token()
	{
		$session = Session::instance();
		
		$token = $session->get(Security::$_logout_token_name);
		
		if ( ! $token)
		{
			$token = sha1(uniqid(NULL, TRUE));
			
			$session->set(Security::$_logout_token_name, $token);
		}
		
		return $token;
	}
	
}