A new way to set up a custom domain in server GTM

Updated May 19, 2026 comments

When setting up server-side tagging, the best practice was configuring a custom domain for your server Google Tag Manager environment. This approach primarily allows setting up first-party cookies, which have a longer lifespan than third-party cookies, enhancing user tracking and data collection consistency.

With the new restrictions coming from Safari, more than just setting up a custom domain is required to prolong cookie lifetime. Even if you map a custom domain, cookies in Safari will be shortened. To make it last longer, you must ensure the custom domain has the same IP address as your website’s primary domain by configuring Own CDN, or use stape Cookie Keeper power-up to store and restore cookies.

However, Google has recently changed the preferred way of mapping a custom domain for the server Google Tag Manager container. Instead of using a subdomain (like sgtm.example.com) they encourage using the same origin (like example.com/sgtm).

With the same origin custom domain for sGTM, you will have the main benefit of server-side tagging - setting up first-party cookies. And with the tagging server using the same origin domain, you do not need to configure any additional settings to prolong cookies. However, mapping the same origin will be more complicated than configuring a subdomain.

How to configure the same origin custom domain in sGTM

Prerequisites

Before you start, make sure you have the following in place:

A server Google Tag Manager container set up on Stape.
A CDN or load balancer capable of forwarding requests, through which all your site traffic is routed.
If you use App Engine, the tagging server should run version 2.2.0 or later.

Note:

For some tags to function properly, your CDN should not apply caching or query string sorting. Cloudflare's Query String Sort or URL normalization, for instance, will interfere with the sendPixelFromBrowser API utilized by some server-side tags.

Configure same origin domain step-by-step

Depending on your infrastructure, you can configure the same origin custom domain using different platforms and services. Here are the guides for each:

Note:

If you're using a platform not listed above, we'd appreciate it if you could send your suggestions to support@stape.io.

Below, we'll walk through the setup using Cloudflare as an example.

For this option to work, all your site traffic must be proxied through Cloudflare – the Cloudflare Workers functionality will then allow you to proxy sGTM requests as well. You should also use SSL/TLS in Full mode; otherwise, same-origin proxying may work via a 301 redirect, which is incorrect.

Step 1. Create a Cloudflare Worker

In the left sidebar, click Compute → Workers & Pages → click Create application → select the Start with Hello World! option.

Step 2. Name and deploy the worker

Add a worker name → click Deploy.

Step 3. Edit the worker code

Decide on the path for your sGTM custom domain – for example, example.com/sgtm, example.com/data, or example.com/metrics.

In the worker settings, click Edit code and paste in JS similar to the example below, where:

/metrics/ is the path you've chosen for your server container.
https://sst.shop.stapedesk.com/ is your tagging server URL.

For the tagging server URL, you have two options:

The default tagging server URL provided by Stape (e.g., https://wapdsrl.ca.stape.io).
The custom subdomain you've set up inside the Stape admin. Using a custom subdomain gives you two advantages: it loads gtm.js and gtag.js from a custom path via the Custom Loader power-up, making tracking scripts unblockable, and it enables long-lived first-party cookies.

If you use a custom subdomain as your same-origin tagging server URL, make sure you've added a custom domain to your sGTM container on Stape and created the required DNS records as described here. Do not use Own CDN with the same origin domain.

export default {
  async fetch(request, env, ctx) {
    let { pathname, search, host } = new URL(request.url);
    pathname = pathname.replace('/metrics/', '/');
    const domain = 'sst.shop.stapedesk.com';
    let newRequest = new Request((`https://` + domain + pathname + search), request);
    newRequest.headers.set('Host', domain);
    return fetch(newRequest);
  },
};

Deploy and save your changes.

Step 4. Add a route to the worker

Go to your sGTM worker → click Domains → Add domain → Route pattern. Select your domain from the list and add the URL you use for the server GTM ending with * (in our example, it's shop.stapedesk.com/metrics*).

Step 5. Create a Configuration Rule

Next to your domain name, click the three dots → Configure Rules.

Click Create rule → Configuration Rules:

Specify any understandable rule name, e.g., sGTM same origin.
Select Custom filter expression.
URI Path starts with /metrics (update this if you're using a different path).
SSL → select the option Full.

Click Deploy.

Step 6. Create a Request Header Transform Rule

Go to Rules → Overview → Create Rule → Request Header Transform Rule:

Enter a descriptive rule name, e.g., sGTM header.
Select Custom filter expression.
URI Path starts with /metrics (update this if you're using a different path).
Set a static header name X-From-Cdn with the value cf-stape.

Save the rule.

Step 7. Update Custom Loader

Once the same origin setup is done, we also recommend updating the Custom Loader power-up for ad blocker protection and implementing it on your site. Don’t forget to specify your Same Origin path in it.

For more information, see our guide on Custom Loader.

Step 8. Add the server container URL in the web and server GTM

1. In your web GTM container, add Google Tag and specify your Measurement ID (any ID works for testing). Set the server_container_url to the same origin path you configured (in our example, it is https://stapedesk.com/metrics).

2. To streamline testing, click Admin → Container Settings → enter the path under Server container URLs.

3. For the testing, the same origin domain (as we show in the step below), you will also need to configure Client (that will transmit data from the web to the server container) and Google Analytics: GA4 tag in the server GTM.

As Client, we will use GA4.

To add GA4 Client in the server GTM, open the clients’ section → Create New client → Select client type Google Analytics: GA4 (Web) → Add client name and click Save.

To configure the GA4 tag, add a new tag with tag configuration “Google Analytics: GA4”, and just specify your Measurement ID in the tag.

And add the trigger for a tag. It should trigger when the client name receives the requests (in our case, the Client is GA4):

Testing your Same Origin setup

Click Preview in both web and server GTM containers.

If everything is set up correctly, the server container should open in preview at the new path you created. If, for some reason, the preview doesn't open at the new path, you can manually enter it in the preview window's URL.

Visit your website. In the server container preview, you should now see an incoming page_view request from your website's real domain.

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