The test is straightforward, but it's a little perplexing if you're
not overly familiar with controlclient.
Signed-off-by: David Anderson <danderson@tailscale.com>
The tests cheat at filling out web forms by directly POSTing to
the target. The target for authURLs has changed slightly, the base
authURL now redirects the user to the login page.
Additionally, the authURL cycle now checks the cookie is set
correctly, so we add cookie jars where necessary to pass the
cookie through.
