Jenkins 2.28. System info attached.

I have projects Upstream and Downstream. I want Upstream to trigger
Downstream when Upstream is stable.

Preferably, I would trigger Downstream as a post-build action of
Upstream. It is also viable for me to trigger Downstream as the
final build-step of Upstream.

Both Upstream and Downstream have configured Build Authorization
Strategy = `Run as User who Triggered Build`.

Nevertheless, whether Downstream is triggered as a post-build action of
Upstream, or as the final build-step of Upstream, the Upstream
configuration page displays the error message:-

You have no permission to build Downstream

When Downstream is triggered as a post-build action of Upstream,
this error message is true. The Upstream build log concludes:

Warning: this build has no associated authentication, so build permissions may be lacking, and downstream projects which cannot even be seen by an anonymous user will be silently skipped
You have no permission to build Downstream
Finished: SUCCESS

When Downstream is triggered as the final build-step of Upstream,
the error message is false. The Upstream build log concludes:

Waiting for the completion of Downstream
Downstream #NN completed. Result was SUCCESS
Build step 'Conditional step (single)' changed build result to SUCCESS
No GitLab connection configured
No GitLab connection configured
Warning: this build has no associated authentication, so build permissions may be lacking, and downstream projects which cannot even be seen by an anonymous user will be silently skipped
Finished: SUCCESS

Apparent bugs are:-

• The error message is spurious, as Upstream should have permission
  to trigger Downstream per the configured Build Authorization Strategy.

• If the error message were not spurious, then Upstream should be unable
  to trigger Downstream either as a build-step or as a post-build action.