Missing priority and issue type icons when exporting Jira Issues Macro to PDF or Doc over https

Summary

When HTTPS is configured for accessing Confluence and Jira externally, but application link is configured over HTTP, exporting Jira Issues Macro in list mode will not render Priority or Type icons. Similarly as described in CONFSERVER-41579 bug

Environment

• Jira and Confluence are behind a proxy and configured for HTTPS access by the client
• Application links is set over HTTP and using a direct connection over specific PORT
• Jira and Confluence Servers can't access each other's External HTTPS URLs

Steps to Reproduce

1. In environment matching above conditions create a Jira Issues Macro list on a blank Confluence page with default columns
2. Export page to PDF or DOC

Expected Results

Macro is rendered in PDF/DOC same way as on original exported page

Actual Results

• PDF will not contain any status icons as flyingpdf is attempting to render them using external URL over HTTPS and not internal application link over HTTP
• DOC document will contain broken image icons where status logos should be present
• The below warning is thrown in the atlassian-confluence.log file when exporting to PDF:

  2018-03-02 07:47:30,089 WARN [http-nio-8090-exec-8] [confluence.extra.flyingpdf.ConfluenceExportUserAgent] getImageResource Could not retrieve image resource https://JIRA_External_URL/images/icons/priorities/none.svg during Confluence export
   -- url: /spaces/flyingpdf/pdfpageexport.action | page: 123456 | traceId: 92ae431b6fb42e50 | userName: user | referer: https://JIRA_External_URL/pages/viewpage.action?spaceKey=SPACE&title=Page | action: pdfpageexport
  2018-03-02 07:47:30,091 WARN [http-nio-8090-exec-8] [confluence.extra.flyingpdf.ConfluenceExportUserAgent] getImageResource Could not retrieve image resource https://JIRA_External_URL/images/icons/priorities/high.svg during Confluence export
   -- url: /spaces/flyingpdf/pdfpageexport.action | page: 123456 | traceId: 92ae431b6fb42e50 | userName: user | referer: https://JIRA_External_URL/pages/viewpage.action?spaceKey=SPACE&title=Page | action: pdfpageexport
  

Note:

The issue is not observed when exporting Jira Issues Macro in single issue view.

Workaround

Allow Confluence server to access Jira over External HTTPS URL