Remote staging authentication error messages aren't clear to the user what is wrong

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 7.0.X EE, Master
• Fix Version/s: 7.0.0 DXP FP25, 7.0.0 DXP FP26, 7.0.X EE, 7.0.4 CE GA5, 7.1.X, Master
• Component/s: Staging
• Labels:
  • QA-NF
  • liferay-digital-enterprise-70-sp5
  • liferay-fixpack-de-25-7010
  • liferay-fixpack-de-26-7010
• Branch Version/s:
  7.0.x
• Backported to Branch:
  Committed
• Story Points: 1.25
• Fix Priority: 3
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/50041

Description:
A user must exist and be authenticated on both the local and remote servers in a remote staging setup. If the user does not exist on the remote server, the only UI tip to this problem is the staging bar exclamation that says "An unexpected error occurred" but this does not give any insights into resolving the error.

Steps to Reproduce:
1. Configure remote publishing with 2 bundles
2. Create a site page and test the remote publish to ensure it is successful
3. In Staging, create a new user test1 with administrator role
4. Log out, and log in as test1
5. Go to staging site page
6. Note the error next to "Go to Remote Live" at the top by hovering over the exclamation mark.

Expected Behavior: Clear error messages explaining what the user did wrong and how they can resolve it
Actual Behavior: Errors are unclear for the user on what next steps to take

Errors/logs

22:46:38,238 ERROR [http-nio-8080-exec-9][view_jsp:637] Unauthenticated user test1
22:46:38,268 ERROR [http-nio-8080-exec-9][SiteAdministrationPanelCategoryDisplayContext:188] Unable to find user [e-mail]

Testing:
Reproduced in 7.0.x - de1b3f18ecf6fc5f2c52e55e54bafa9f51693857
(The fix to the staging bar error, LPS-69913, is scheduled to be backported)

Reproduced in master - 24c136c8850a46a9eb88ff12c8e1538e2d5996fa