When the POST to the CLI's localhost callback endpoint results in a
non-2XX status code, then treat that as a failed login attempt and
automatically show the manual copy/paste UI.
This is a new pacakge internal/oidc/provider/formposthtml containing a number of static files embedded using the relatively recent Go "//go:embed" functionality introduced in Go 1.16 (https://blog.golang.org/go1.16).
The Javascript and CSS files are minifiied and injected to make a single self-contained HTML response. There is a special Content-Security-Policy helper to calculate hash-based script-src and style-src rules.
This new code is covered by a new integration test that exercises the JS/HTML functionality in a real browser outside of the rest of the Supervisor.
Signed-off-by: Matt Moyer <moyerm@vmware.com>
