Tapping "Authenticate" on a Jira (and Jira Chart) macro from another instance does not work

Issue Summary

When a Confluence-only (without Jira in the same tenant) instance is integrated with Jira via application links, if a page has the Jira chart macro (or simply the Jira macro) pointing to the linked Jira instance, it will display an "Authenticate to see issue details" message while viewing the page.

When tapping the "Authenticate" button, one of the following errors can happen:

• A browser error saying "The site can't be reached" is displayed.
• A browser error saying "Took too long to respond" is displayed.

For internal Atlassian users, a "We'll be back in a flash" message is displayed.

Steps to Reproduce

1. As an administrator of a Confluence-only instance (it should not have Jira added to the instance as well), go to the Application Links configuration from the administration (gear icon at the top-right).
2. There, configure the application link to the Jira instance.
3. Once it is finished, add the Jira Chart macro into a Confluence page. While on the macro configuration, this process will ask the user to Authenticate in order to retrieve the details.
4. Authenticate to be able to add the macro and the results.
5. Have a different user that has access to both instances (Jira and Confluence) accessing the page and tapping the Authenticate button.

Expected Results

The user should be redirected to the "OAuth dance" page in order to tap Allow and have the content displayed.

Actual Results

A browser error happens and the authentication does not work.

Additional notes:

• The URL in the authentication is something similar to the following:

confluence-prod-REGION-NUMBER-NUMBER.prod.atl-paas.net

Workaround

Edit the page and then, the Jira (and Jira chart) macro. This will present the flow to authenticate as it is done via the Jira issues macro:

1. When editing the macro (while editing the page), tap the Login & Approve button.
2. There, follow the flow and tap Allow
3. Once the content is displayed, close the draft (or the tab) and go back to the published mode of the page.
4. Refresh it