如何为带密码的表单设置validation.yml（Symfony2）

I would like to know how to check whether the entered by user passwords are the same? I need solution for validation.yml file. I have something like that:

validation.yml:

ZaqU\MyBundle\Entity\SignupForm:
    properties:
        password:
            - NotBlank:
                message: trans.validation.password.notBlank
            - Length:
                min: 8
                max: 30
                minMessage: trans.validation.password.minLength
                maxMessage: trans.validation.password.maxLength
        rpassword:
            - NotBlank:
                message: trans.validation.rpassword.notBlank

What I should add to rpassword from this list: http://symfony.com/doc/current/reference/constraints.html ?

If you use the form framework together with the validator, you can use the repeated field type.

If you want to use the validator alone, you can use one of these constraints:

• Callback
• Expression

You'll find the constraint reference here: http://symfony.com/doc/current/reference/constraints.html