Activity Stream gadget throws "The resource rest/webResources/1.0/resources, cannot be found." error

How to reproduce this problem

Have Confluence 6.2.3 + JIRA 7.3.8 installed and configured with application links:

1. Create a dashboard in JIRA
2. Click Add Gadget, then Manage gadgets to add the Activity Stream Gadget with the gadget URL served from confluence
3. Add the Activity Stream Gadget to a JIRA dashboard, and observe the error message about resource cannot be found.

The issue could be reproduced by adding the Activity Stream gadget into a page in confluence.

Diagnosis

Within Jira:

1. Navigate to Jira Administration » System » Logging and profiling
   • Enable HTTP Access logging

Within Confluence:

1. Add the Activity Stream Gadget to a JIRA dashboard, and observe the error message about resource cannot be found.

On Jira side:

1. Open up $JIRA_HOME/log/atlassian-jira-http-access.log
2. Search for rest/webResources/1.0/resources
   atlassian-jira-http-access.log

   127.0.0.1 i843x1060x1 admin [02/Nov/2017:14:03:22 +1100] "POST http://localhost:8080/jira/jira/rest/webResources/1.0/resources HTTP/1.1" - - - "http://localhost:8751/jira/plugins/servlet/gadgets/ifr?container=atlassian&mi...
   127.0.0.1 o843x1060x1 admin [02/Nov/2017:14:03:22 +1100] "POST http://localhost:8080/jira/jira/rest/webResources/1.0/resources HTTP/1.1" 404 0 0.0010 "http://localhost:8751/jira/plugins/servlet/gadgets/ifr?container=atlas...
   

3. You can see that the URL requested into Jira by confluence has the Jira web context "/jira" incorrectly added twice resulting in a HTTP 404 Not Found Error

Cause

Confluence is incorrectly doubling up the Jira web context path when hitting the Jira rest/webResources/1.0/resources REST call.

Workaround

Some people are able to work around the issue by creating a redirect rule as follows:

Pattern: \bconfluence/(\bconfluence.*)
Rewrite URL: http://localhost:8090/\{R:1}

Essentially chopping off the second /confluence.
NOTE: You must move this rule above the rewrite rule that sends normal traffic to confluence.

The same for double jira.