Shorten the URL to be used by the user and automatically use the
returned code by the server. The browser is opened on
`http://(bindaddress)/auth`, and redirected to the actual URL. When
the code is returned it is automatically inserted, instead of
requiring a copy+paste.
This is also a workaround for the "open" package, which escapes "&"
wrongly on Windows, so the opened URL's are invalid.