Enable Private Click Tracking, Attribution Reporting API and Ping on `a` tags

Description

As the web is transitioning to becoming more private, new technologies are emerging to enable private click tracking and click attribution. This is done with attributes on a link tags. Unfortunately, implementing these private click tracking methods invalidates AMP pages.

Please consider enabling the following attributes on a tags:

• impressiondata
• conversiondestination
• impressionexpiry
• reportingorigin
• attributionsourceid
• attributeon
• ping

Alternatives Considered

None, as adding the attributes renders the AMP pages invalid.

Additional Context

Private Click Measurement spec Attribution Reporting API spec

This was initially brought up in #34449 , I just started implementing a proof of concept today and saw the page becoming invalid.

[kristoferbaxter]

On the ping attribute, it’s also part of the WhatWG html specification.

https://html.spec.whatwg.org/multipage/links.html

The ping attribute, if present, gives the URLs of the resources that are interested in being notified if the user follows the hyperlink. The value must be a set of space-separated tokens, each of which must be a valid non-empty URL whose scheme is an HTTP(S) scheme. The value is used by the user agent for hyperlink auditing.

Making it valid, and potentially ensuring it’s a valid space-separated token list of https urls seems like a good idea.

[maudnals]

(hi there, Chrome web DevRel here, I’m working on this API, chiming in as @alanorozco pinged me)

• ping is not part of Chrome’s Attribution Reporting spec (maybe it’s part of other specs). It looks like it’s not part of WebKit’s latest PCM spec, either (see spec). You should be able to safely ignore it for Attribution Reporting support.
• attributeon has been deprecated in favor of attributiondestination. I can confirm with certainty that attributiondestination is the correct attribute for Chrome. WebKit’s spec seems to be using attributiondestination as well.
• I’m unsure about attributionsourceid. It looks like Chrome is using attributionsourceeventid and WebKit attributionsourceid. I’ll explore why these are different and whether they ned to be aligned, but if possible in the meantime it may make sense to support both attributes.