SPNEGO login flow: Enforce SPNEGO by condition

[Daniel Lutz]

On 2015-12-01 at 17:52, Cantor, Scott wrote:
> Specifically, check for the missing cookie and set it if the user agent
> matches in a script auto-run by the password form. The user won't see any
> difference.

I think there's more to do besides setting the cookie:
After having set the cookie, the script needs to submit an
"authn/SPNEGO" event to the flow to make the SPNEGO login flow
be run as an extended flow.

Furthermore, the script needs to avoid an endless loop.
If the SPNEGO login flow is run as an extended flow,
it must not be run again after having failed.
I think that I can check for existing errors in $authenticationErrorContext.
If there are errors, auto-login must not occur.

I'll try it this way.

-- Daniel