SPNEGO login flow: Enforce SPNEGO by condition

[Daniel Lutz]

In the meantime, I've implemented a possible solution.

It's a velocity template that can be included in login.vm.

It's available here:

https://forge.switch.ch/redmine/projects/idp_v3_kerberos_authentication_flow/repository/entry/src/main/resources/views/login-spnego.vm

Instructions how to use it are given in the header of the template.

What do you think about it?
If this is usable, I will add it to the documentation.

-- Daniel