Overview

MetaRouter’s cross-domain identity feature enables consistent, anonymous device-level user identification across multiple domains you own, without relying on personally identifiable information (PII).

The solution works by setting a first-party HTTP cookie scoped to one of your domains. Each site stores the returned identifier locally for use in analytics and event delivery. No identity profiles are ever stored in MetaRouter, utilizing the user’s browser as the primary means to stitch together a cross-domain identity of the user.

This ID is most commonly used for identity joins across user sessions in Customer Data Platforms and analytics solutions, allowing you to understand your customers’ behavior across all of your owned top-level domains.

Prerequisites

• Your MetaRouter service agreement includes Cross-Domain Identity Syncing.
• You must have the Sync Injector implemented on the websites where you would like to maintain a shared cross-domain identifier.

Configuring Cross-Domain Syncing

Configuring a cross-domain sync requires the following steps:

1. Navigate to the Analytics.js File Builder pages for the pipelines tied to the websites where you would like to implement your cross-domain ID sync.
2. Scroll down to the Cross-Domain Identity Sync section of the File Builder.
3. Input one of the URLs where a cross-domain ID sync will be taking place. We recommend choosing the URL with the most website traffic. Ensure this URL is consistent across all of your files.
   1. The URL should be formatted using the following structure: https://Your_Cluster_Domain/v1/cross_domain_direct/id
4. Save and deploy your files.
5. Verify that the context.providers.crossDomainDirect.idis being tracked and is the same across all websites.

How Cross-Domain Syncing Works

On a user’s first visit to any configured website, MetaRouter generates a unique cross-domain identifier and stores it in the Browser Storage Location you configured within the Advanced Settings section of the File Builder. Also upon the user’s first visit to any configured website, MetaRouter sets a server-side cookie on domain you designated in the Cross-Domain Direct Identity Sync section.

When that same user later visits another site configured for cross-domain syncing, the browser makes a request to the URL specified within the Cross-Domain Identity Sync. Because a server-side cookie has already been set and scoped to that domain, it can be read and used to look up the existing cross-domain ID.

The shared domain responds with the previously assigned identifier, which is then written to the new site’s first-party storage and used as the cross-domain ID moving forward.

Using the Cross-Domain ID

To use the Cross-Domain IDs generated by MetaRouter, you must expose the Cross-Domain ID to your downstream destinations.

The Cross-Domain ID is included in the event payload generated by your Analytics.js file, under:

context.providers.crossDomainDirect.id

Once available, the Cross-Domain ID can be mapped to an appropriate identifier field in each destination. The specific field and configuration required will vary by destination.

After the Cross-Domain ID is successfully received by a destination, you can apply any destination-specific logic—such as identity stitching, attribution, or analytics—using the Cross-Domain ID as a consistent identifier across domains.

Limitations

Safari ITP

Safari enforces strict privacy protections that limit how cookies can be used across domains. As part of Intelligent Tracking Prevention (ITP), Safari restricts access to cookies in third-party contexts, even when those cookies are set by a first-party domain elsewhere.

Because MetaRouter’s cross-domain syncing relies on a browser request to a shared domain in order to retrieve a previously assigned identifier, Safari does not allow the server-scoped cookie on that shared domain to be read in this context. As a result, the Cross-Domain ID cannot be retrieved or reused when users navigate between sites in Safari.

This behavior is enforced by the browser and applies broadly to any solution that relies on third-party cookie access for cross-domain identification.