Playing around with "tailscale.com/tsnet", it's cool!

tsnet.go

/*
Usage of INET (Uses TSKEY environment variable)

...
if ips := inet.Wait(context.Background()); len(ips) > 0 {
	log.Printf("connected to tailscale (ips=%v)", ips)
} else {
	log.Printf("not connected to tailscale")
}
defer inet.Shutdown()
...
resp, err := inet.HTTPClient().Get("https://tailscale.com")
...
*/

// Package inet is a utility package which creates a Tailscale instance automatically,
// and exposes proper dialers which allow this binary to access a Tailscale network.
package inet

import (
	"context"
	"net/http"
	"net/netip"
	"os"
	"time"

	"github.com/pkg/errors"
	"tailscale.com/tsnet"
)

var server = &tsnet.Server{
	AuthKey:   os.Getenv("TSKEY"),
	Logf:      noopLogger,
	Ephemeral: true, // We're only running this in the context of this Go binary.
}

// Status returns the status of the Tailscale server.
func Status(ctx context.Context) (string, []netip.Addr, error) {
	client, err := server.LocalClient()
	if err != nil {
		return "", nil, errors.Wrap(err, "failed to get local client")
	}

	resp, err := client.Status(ctx)
	if err != nil {
		return "", nil, errors.Wrap(err, "failed to get status")
	}

	return resp.BackendState, resp.TailscaleIPs, nil
}

// Wait waits for the server to come online. If the server failed to come online for any reason,
// a nil set of addresses will be returned (indicating that we don't have a Tailscale IP, and are
// thus unable to access machines on the Tailscale network).
func Wait(ctx context.Context) []netip.Addr {
	if _, ok := os.LookupEnv("TSKEY"); !ok {
		return nil
	}
	for {
		status, ips, err := Status(ctx)
		if err != nil {
			return nil
		} else if status == "Running" && len(ips) > 0 {
			return ips
		}
		time.Sleep(time.Second)
	}
}

// HTTPClient returns a http.Client which can be used to make outgoing requests to machines on the
// Tailscale network. If the Tailscale server is not running, this will return http.DefaultClient.
func HTTPClient() *http.Client {
	return &http.Client{
		Transport: &http.Transport{
			DialContext: server.Dial,
		},
	}
}

// Shutdown closes the Tailscale server, if it is running.
func Shutdown() error {
	return server.Close()
}

func noopLogger(format string, args ...any) {}

Also, just a note: This is probably super un-idiomatic & not how this package was intended on being used. We're going to use this code in production, but that's because we like to live on the edge (it makes things more fun).