Nick Khyl 94f4f83731 ipn, ipn/ipnlocal: reduce coupling between LocalBackend/profileManager and the Windows-specific "current user" model
Ultimately, we'd like to get rid of the concept of the "current user". It is only used on Windows,
but even then it doesn't work well in multi-user and enterprise/managed Windows environments.

In this PR, we update LocalBackend and profileManager to decouple them a bit more from this obsolete concept.
This is done in a preparation for extracting ipnlocal.Extension-related interfaces and types, and using them
to implement optional features like tailscale/corp#27645, instead of continuing growing the core ipnlocal logic.

Notably, we rename (*profileManager).SetCurrentUserAndProfile() to SwitchToProfile() and change its signature
to accept an ipn.LoginProfileView instead of an ipn.ProfileID and ipn.WindowsUserID. Since we're not removing
the "current user" completely just yet, the method sets the current user to the owner of the target profile.

We also update the profileResolver callback type, which is typically implemented by LocalBackend extensions,
to return an ipn.LoginProfileView instead of ipn.ProfileID and ipn.WindowsUserID.

Updates tailscale/corp#27645
Updates tailscale/corp#18342

Signed-off-by: Nick Khyl <nickk@tailscale.com>
2025-04-10 12:24:00 -05:00
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