UI authentication via via CLI should allow user to print the URL to stdout

[galeep]

Proposal

nomad ui -authenticate should be able to print the URL/otp as a fallback (or with a --stdout flag)

Use-cases

As a practitioner, I want to be able to authenticate to the Nomad UI even when I'm executing nomad from a headless session (i.e., ssh/cloud shell/otherwise not running a display manager.)

In my particular case, I was executing the command from an ssh session, and was accessing the GUI through a tunnel. This is how I normally use Nomad.

Attempted Solutions

Currently, this is handled via xdg-open with no fallback mechanism.
If xdg-open is not present in the user's path, the user will see an error. The URL will not be printed.
if xdg-open is present, the user will see a message that indicates the URL will be opened, but nothing will happen.

The user requesting this already has access to the secret.

[tgross]

Currently, this is handled via xdg-open with no fallback mechanism.
If xdg-open is not present in the user's path, the user will see an error.

Just for clarity for whomever ends up implementing this, we use xdg-open only on Linux. We're using https://github.com/skratchdot/open-golang to use the OS-specific open, xdg-open, or start command. So we'll want to catch the error condition where the user has a headless environment to capture the token (or use an explicit flag as suggested here).

[lgfa29]

Closed by #11213

[github-actions]

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