Ability to connect to tailnet

[gabegorelick]

Is your feature request related to a problem? Please describe.

It's fairly common for Terraform to need to connect to resources that are not accessible to the machine running terraform. This is documented pretty well for SSH jump hosts in hashicorp/terraform#8367, but the same applies to Tailscale. In other words: there should be a way to use Tailscale to let Terraform connect to resources on your tailnet.

Often times, you can just run tailscale up before you run terraform. But that's not possible in environments like Terraform Cloud.

Describe the solution you'd like
Some kind of resource or module that connects to a tailnet:

# This would effectively run `tailscale up`.
resource tailscale_connection {
  authkey: "emphemeral_key"
}

provider mysql {
  # This now works because we're connected to the tailnet.
  endpoint = "private_address"
}

Additional context
Prior art: https://github.com/jaysonsantos/terraform-provider-jumphost and https://github.com/flaupretre/terraform-ssh-tunnel