Host users take ownership of existing home directories

[eriktate]

This PR updates CreateHomeDirectory such that it takes ownership of existing home directories and their contents. I originally thought we were already chowning the directory contents and we were just omitting the directory itself. However, I realized while implementing that this only happened for the files copied from skel so we'll need to figure out if this is something we want to move forward with or not

changelog: Allows host user creation to take ownership of existing home directories on behalf of the newly created user.

[espadolini]

Do we have to recursively chown the whole home directory tree rather than make just the directory owned, readable(?) and accessible by the user? What if there's something in there that's owned by root and is not supposed to be read by the user?

If we do this we should definitely at least check and see if the uid that owns the directory isn't a user that already exists in the system.

[espadolini]

Why is this necessary? Collecting a slice of unbounded size of paths doesn't feel great.

[eriktate]

It probably isn't 🤔 This was copied from the existing function that used to be in utils, but I don't see any reason to keep this behavior

[eriktate]

Do we have to recursively chown the whole home directory tree rather than make just the directory owned, readable(?) and accessible by the user? What if there's something in there that's owned by root and is not supposed to be read by the user?

If we do this we should definitely at least check and see if the uid that owns the directory isn't a user that already exists in the system.

I think it depends on the expected behavior here. As far as I understand, the primary usage would be in moving users over to teleport that were previously managed some other way. Which would benefit from taking ownership of everything since it's meant to be effectively the same user. @rosstimothy do you think it would be acceptable to only take ownership of the directory and not the contents?

Validating the UIDs are "safe" to overwrite is a great idea 👍

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