Short description of your issue:

Dynamically insert content into anchor href on click

How do we reproduce the issue?

IOS safari doesn't allow third part cookies to get set and because of this we are not able to stitch the session and get clear metrics on the source attribution & bounce rate.

1. Visit https://www.google.com/amp/m.ebay.com/sch/amp/Digital-Cameras/31388/bn_779/i.html on IOS safari
2. Tracking call will be made on this page with endpoint "pulsar.ebay.com". This call takes care of setting the GUID on ebay.com domain. But in IOS safari this doesn't happen

What browsers are affected?

IOS safari

Which AMP version is affected?

It always broken

Suggestion to fix the issue

Provide a way to attach dynamic content to anchor href click this can include 2 types of values

1. Static value that need to be appended to the URL like _trksid=p2376289.m4213.l8401
2. Dynamic data like gclinetId=CLIENT_ID which would be the google client id

Prototype: https://s.codepen.io/boomerang/iFrameKey-ab729c71-f09f-b030-3156-c3b527089abc/index.html
CodePen: https://codepen.io/rajkumarsrk/pen/GWxyoq