How to specify Composer install path?

I have this definition:

{
    "repositories": [
        {
            "type": "package",
            "package": {
                "name": "symfony/sfGuardPlugin",
                "version": "4.0.2",
                "dist": {
                    "url": "http://plugins.symfony-project.org/get/sfGuardPlugin/sfGuardPlugin-4.0.2.tgz",
                    "type": "tar"
                }
            }
        }
    ],
    "require": {
        "symfony/sfGuardPlugin": "4.0.*"
    }
}

I am using Symfony 1, and I'd like to install them on plugins/sfGuardPlugin/. How do I specify this?