https://edps.europa.eu/sites/edp/files/publication/16-11-07_guidelines_web_services_en.pdf
incl. also interesting links to other EU papers (e.g. on cloud)
Sadly from Nov 2016, so with GDPR in mind, but not in force, yet.
Covered technologies include
Cookies
Scripts (such e.g. JavaScript code) and components (such as browsers plugins) to be executed on the client side.
Web caching mechanisms
HTML5 local storage
“Device fingerprinting”
“Canvas fingerprinting” and “Evercookies”
Web beacons