Application Link - Oauth impersonation doesn't work as expected

Step to reproduce:

1. Install Confluence and JIRA;
2. Create an Application Link using OAuth with Impersonation;
3. Try to retrieve any information from Jira through Confluence (i.e. Jira issues macro) or Link a Confluence page into a Jira Issue;

Expected behavior

It should display data from the remote application without authentication request.

Actual behaviour

The "Login & Approve" message appears requiring authentication against the linked application before we can see the content.

Business impact

Currently, OAuth system requires one token per user per gadget, so the user has to authenticate again for every gadget to generate the token to grant the access. In some cases (https://jira.atlassian.com/browse/CONFSERVER-52397) there's no "Login & Approve" message, and the user has to get the token elsewhere.