Extend `Logged in with gh` to support GHE

[andyfeller]

Describe the feature or problem you'd like to solve

As a GHE user, I would like copilot to leverage my ghe.com session from gh like it does when I'm authenticated with my github.com session

Proposed solution

As a GitHub CLI user, I am authenticated with both GitHub.com and GHE accounts. gh determines the appropriate credentials based on various factors:

1. Local git repository remotes
2. Command line arguments that capture HOST/OWNER/REPO
3. GH_HOST env var

The benefit is a uniform streamline experience for both GitHub Copilot CLI and GitHub CLI users.

Example prompts or workflows

No response

Additional context

When I launch copilot authenticated to github.com:

When I launch copilot authenticated to GHE tenant:

[andyfeller]

Please let me say I know this is a little complicated especially with multi-account support across the 2 CLIs. In gh when multiple hosts are authenticated, it defaults to github.com unless 1) the local git repository remotes point elsewhere, 2) some --hostname flag, or 3) GH_HOST env var is set.

That last option might be an okay short term solution: copilot could inspect and leverage GH_HOST to decide which gh session to use for copilot auth. 🤷

[examon]

This is now supported. Setting the GH_HOST environment variable to your GHE hostname (e.g., mycompany.ghe.com) directs the CLI to use those credentials for authentication and API requests against your GHE tenant. The variable is documented in copilot help under environment variables. Automatic host detection from git remotes is not yet implemented, so GH_HOST does need to be set explicitly for now. If you believe this is not fully resolved, please feel free to reopen.