Improve error message for "juju register"

[Leon]

I did "juju add-user" on one controller and "juju register" elsewhere, per doc:

https://juju.is/docs/juju/manage-controllers#heading--register-a-controller

The register command fails with this error:

ERROR Provided registration token may have been expired.
A controller administrator must reset your user to issue a new token.
See "juju help change-user-password" for more information.

But it's unclear what exactly failed. The hint seems irrelevant to my situation.

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I have a multipass VM with juju (outer VM), and inside it another multipass VM with juju and microk8s and prometheus (inner VM).

After "ip route add" in the outer VM, I am able to curl the api-endpoint of the inner vm controller, but "juju register" fails with the error above. It would be great if the error message could be slightly more tailored to the situation. For example:

ERROR Unable to reach controller endpoint at 10.152.183.146:17070.

[Leon (sed-i)]

BTW, I do not see "while validating secret key" in syslog/journalctl.

https://github.com/juju/juju/blob/e86a0e81b5b2a4ba554380373acb066f333b72f2/cmd/juju/controller/register.go#L381

[Joseph Phillips (manadart)]

Yes. This prose is generated without interrogating the actual error originating deeper in the call stack.

It would be simple enough to make it conditional.