wcmo_redirect_url.php

<?php
/**
 * Find which category is protected by a given password
 * @return term_id
 */
function prefix_get_product_category_by_password( $password ) {
	$terms = get_terms( array( 
		'taxonomy' => 'product_cat'
	) );
	if( $terms ) {
		foreach( $terms as $index=>$term ) {
			$term_id = $term->term_id;
			$passwords = get_term_meta( $term_id, 'wcmo_passwords', true );
			$passwords = explode( "\n", str_replace( "\r", "", $passwords ) );
			if( $passwords ) {
				foreach( $passwords as $p ) {
					if( $p == $password ) {
						// This is the ID of the protected category
						return $term_id;
					}
				}
			}
		}
	}
	return false;
}

/**
 * Filter the redirect URL to redirect to category protected by specific password
 */
function prefix_redirect_url( $url, $password ) {
	if( $password ) {
		$cat_id = prefix_get_product_category_by_password( $password="music" );
		if( $cat_id ) {
			$url = get_term_link( $cat_id );
		}
	}
	return $url;
}
add_filter( 'wcmo_redirect_url', 'prefix_redirect_url', 10, 2 );