SPNEGO login flow: Enforce SPNEGO by condition

[Daniel Lutz]

Cantor, Scott schrieb am 01.12.15 um 18:34:
> Are we currently clearing the cookie or setting it to a zero/false value?
> That might be a better approach to avoid loops.

On failure, the SPNEGO login flow clears the cookie (via
CookieManager.unsetCookie()). So we can't decide whether the cookie has
never been set or whether an error occured.

(Now I realize that it would have been useful to explicitly set
a value of "0" on failure. I didn't think of such a usage.)

-- Daniel