How To Migrate Cookie Domain And Retain The Value

Is it somehow possible to migrate domains from a cookie? I have a trackingscript witch sets a cookie on the domain of the tracking script(server side, RoR backend) lets say mytrac

Solution 1:

In your client side JavaScript, generate a unique ID. Then create an iframe with a source pointing to a script on mytracking.com and the unique ID as a parameter.

var ifrm = document.createElement('iframe');
ifrm.setAttribute('src', 'mytracking.com/storecookie.rb?uuid=<UUID>');
document.body.appendChild(ifrm);

Now the storecookie.rb script can access the cookie value on the mytracking.com domain and writes it to a database along with the UUID that you generated.

Now, in your client side JavaScript, you fetch() another script, for example mytracking.com/readcookie.rb?uuid=<UUID> that retrieves the matching cookie value from the database. With the value in your client side JS, you can simply create a new cookie with the correct domain.

Unfortunately that process is a bit convoluted, but cross-domain security prevents setting a cookie for another domain.