Make atServer-to-atServer issues easier to diagnose

[gkc]

Is your feature request related to a problem? Please describe.

It is difficult to diagnose when an atServer to atServer connection fails due to, for example, an invalid client cert being presented.

Describe the solution you'd like

If an atServer @alice rejects a connection from another atServer @bob, for example because @bob's client cert is invalid, then at a minimum an appropriate SEVERE error should be logged, and ideally the exception should be visible to @bob's atClients

Describe alternatives you've considered

No response

Additional context

No response