Add Slug Metabox to posts for contributors

I approached by doing the opposite with using remove_meta_box() for the Slug metabox if the user is not an administrator or contributor:

add_action( 'admin_menu', 'wpse_237291_remove_slug_metabox' );
function wpse_237291_remove_slug_metabox() {
    $user = wp_get_current_user();
    $allowed_roles = array( 'administrator', 'contributor' );

    if ( !array_intersect( $allowed_roles, $user -> roles ) ) {
        remove_meta_box( 'slugdiv', 'post', 'normal' );
    }
}