WordPress: Protect custom post type with a predefined password

<?php
/**
 * WordPress:
 * Protect custom post type with a predefined password
 */
add_action( 'the_post', function( $post ){
    if ( $post->post_type == 'gallery' ) { // Write the custom post type ID here
        $post->post_password = 'MyP@sSW0rD'; // The predefined password goes here
    }
} );