How to set up a cross-domain tracking?

Cross-domain tracking allows you to follow a visitor, and his behavior, from one domain to another domain. To perform insightful analyses in Piano Analytics, it implies that the Visitor ID remains the same in both domains.

Note: it is unnecessary to have both domains set up with the same site ID in Piano Analytics because visitor IDs are unique at the organization level and will be correctly deduplicated when running analyses on a group of sites. However, using a single site ID usually eases the data analysis and is usually preferred.

Privacy context

Before going further with the technical implications, setting the Privacy context around cross-domain tracking is important.

If you benefit from the e-Privacy Exemption solely, cross-domain tracking is prohibited and should not be set up.
If you benefit from the e-Privacy Hybrid Measurement, cross-domain tracking can be set up for visitors who have consented ("optin" visitor mode). Please refer to the DPO of your company for any questions or concerns about the privacy context of your different domains.

Technical Implementation

Two options are technically feasible to achieve cross-domain tracking:

1/ Forcing the idclient value

If your site is using client-side cookies (“idclient” value sent in the hit), you will need to retrieve the Visitor ID from Domain A, transit it to Domain B (in a querystring of the URL for instance) and use this value to set the Visitor ID of Domain B.

🏷️ Piano Analytics SDK

pa.getVisitorId() > method to retrieve the idclient from the _pcid cookie on domain A
pa.setVisitorId(visitorId) > method to set the idclient on domain B (must be performed before sending the first event on domain B)

Documentation

🏷️ SmartTag

1/ Retrieve the visitor ID from the atuserid cookie or using the method:

JS

tag.clientSideUserId.get();

2/ Set the idclient on domain B with the following method:

JS

var context = {
userIdentifier: 'VisitorID'
};
var tag = new ATInternet.Tracker.Tag(config, context);

or

JS

tag.clientSideUserId.set('userID');

Documentation

Note: by forcing the idclient on domain B, you may increase the number of Unique Visitors on your site (if the visitor had id 12345 in the past, and you now force id 67890 of domain A.) You may want to perform a check on the existence of the Visitor cookie. If a cookie already exists, you may want to either erase it to focus on cross-domain analyses, or keep it to focus on the real count of Unique Visitors.

2/ Using server-side cookies

Using server-side cookies (3rd party) will set the cookie on the collection domain, most often pa-cd.com, and the value will be shared across all sites of an organization (all sites using server-side cookies).

Note: this set up isn't possible if you use the Exemption or Hybrid Measurement, in so far as client-side cookies are required with the Privacy plugin.

Warning: 3rd part cookies aren't allowed on all browsers. Safari and Firefox, for instance, have disabled the use of such cookies. We do not recommend this set up as it will not work evenly, and Google will eventually suppress 3rd party cookies in 2024.

🏷️ Piano Analytics SDK

JS

window._pac = window._pac || {};
_pac.isVisitorClientSide = false
<script type="text/javascript" src="https://tag.aticdn.net/piano-analytics.js"></script>

Documentation

🏷️ Smarttag

JS

var config = {ClientSideUserId: {clientSideMode: 'required'}};
var tag = new ATInternet.Tracker.Tag(config);

Documentation (the "required" mode will switch to server-side cookies when they are compatible with the browser.)