How to add Redirect Url for App Proxy Application when User logs in

[colchuck]

I have a storefront in Shopify, and one of the tabs is a nextjs app which is hosted with app proxy. I have everything working, and I am trying to support users who are unauthenticated with Shopify. 

I can detect if they are not authenticated and show a notification with a "Click here to login" link. The problem is, it always takes them to the orders page after the login, not back to the route they were on when I initiated the flow. I have tried a number of solutions but nothing is working including. Below is the loginUrl I am using in my <a> tag as the href. The behavior described happens after the user clicks on the anchor.
1.) 

const loginUrl = `<STOREFRONT_DOMAIN>/customer_authentication/redirect?return_to=${currentUrl}`;

This approach gets them to the login page, they login, and it takes them to the orders page, instead of to my "current URL" value.

2.) 

const loginUrl = `<STOREFRONT_DOMAIN>/customer_authentication/login?return_to=${currentUrl}`;

I found this URL on line for some liquid apps or whatnot, but when I use this I get a Bad Request message in the main page.

Any help would be greatly appreciated!

[colchuck]

I figured it out:

const storeDomain = getDomainUrl();

// The relative path you want to redirect to (the app proxy path):

const appProxyRoute = '/apps/rod-builder';

// Build the login URL that Shopify will accept

// Important: The return_url must be relative (no domain).

const loginUrl = `${storeDomain}/customer_authentication/login?return_to=${encodeURIComponent(appProxyRoute)}`;