JavaScript API doesn't work if Jira runs in iframe itself

Created from https://ecosystem.atlassian.net/browse/ACJIRA-2613

Issue Summary

Our customers want to embed our Jira app’s UI into Confluence pages. To do so, they add an iframe using Confluence’s built-in iframe macro, pointing to the respective Jira URL (e.g. https://foo.atlassian.net/projects/FOO?selectedItem=com.atlassian.plugins.atlassian-connect-plugin:app.jxl).

In this setup, the Connect JavaScript API - while being loaded seemingly successfully - doesn’t work; the various callbacks, like window.AP.getCurrentUser, simply never resolve.

To verify, call

window.AP.getCurrentUser((x) => console.log(x));

from the Connect iframe's console. It works if Jira runs in its own browser window, but doesn’t resolve if Jira runs within the iframe.

There's suspicion that Connect gets confused about to the two nested iframes: First, Jira in Confluence, and then our app in Jira.

Steps to Reproduce

1. Confluence’s built-in iframe macro, pointing to the respective Jira URL (e.g. https://foo.atlassian.net/projects/FOO?selectedItem=com.atlassian.plugins.atlassian-connect-plugin:app.jxl).
2. Call from the Connect iframe's console:

   window.AP.getCurrentUser((x) => console.log(x));

Expected Results

It resolves within Jira iframe.

Actual Results

It doesn’t resolve if Jira runs within the iframe. 

Workaround

Currently there is no known workaround for this behavior. A workaround will be added here when available

Additionally it blocks important use cases for customers.