koa-shopify-auth too many redirects

[Mykhailo]

Hello community!

I am trying to deploy Node Shopify Public App on different domains for Frontend and Backend.

Each time I call https://<MY_BACKEND_PATH>/auth?shop=<MY_SHOP> I get HTTP 302 with Location same as original request https://<MY_BACKEND_PATH>/auth?shop=<MY_SHOP>

I have NextJS run as static site on another domain. I have provided all correct Env variables to my Backend. I am using latest Shopify CLI. I have updated my Partner Dashboard correctly.

All is working fine with shopify node server i.e. with ngrok but fails in real life.

What have I missed?

[Mykhailo]

ok, found issue... that's because I need to use prefix for Koa auth lib. Since I need to prepend each request with /dev/index I enforced to add 

prefix: "/dev/index/

to my createShopifyAuth method. Any idea how to overcome this?

server.use(
  createShopifyAuth({
    prefix: "/dev/index",// I need this to have /dev/index/auth/inline redirect but not /auth/inline since it is not served by my Backend
    async afterAuth(ctx) {
      console.log("afterAuth", ctx);
      // Access token and shop available in ctx.state.shopify
      const { shop, accessToken, scope } = ctx.state.shopify;
      const host = ctx.query.host;
      ACTIVE_SHOPIFY_SHOPS[shop] = scope;

      const response = await Shopify.Webhooks.Registry.register({
        shop,
        accessToken,
        path: "/webhooks",
        topic: "APP_UNINSTALLED",
        webhookHandler: async (topic, shop, body) =>
          delete ACTIVE_SHOPIFY_SHOPS[shop],
      });

      if (!response.success) {
        console.log(
          `Failed to register APP_UNINSTALLED webhook: ${response.result}`
        );
      }

      // Redirect to app with shop parameter upon auth
      ctx.redirect(`${process.env.BACKEND_URL}/?shop=${shop}&host=${host}`);
    },
  })
);

[Mykhailo · Accepted solution]

ok, seems having prefix in afterAuth is bad idea since it will not work for case when Koa deployed not on root /. Creating domain name and assigning it to my host's / solved the problem