[kitten] CredUI

[Luke Howard <[e-mail]>]

Announcing a new open source project is pretty off-topic for ietf-kitten so I'll keep it brief and to a URL:

	https://github.com/PADL/CredUI

On-topic is that it does offer a way (much inspired by the equivalent SSPI APIs) to do interactive credential acquisition with prompting with very limited changes to GSS-API. Essentially the changes are:

* a new supplementary status code, GSS_S_PROMPTED_NEEDED, indicated the prompting is needed (this can be combined with other GSS-API error codes). This can be returned by gss_init_sec_context().
* an API/SPI to acquire a credential given an arbitrary dictionary (currently we implemented this using gss_set_cred_option(), as that can output a credential, but a new entry point would be cleaner)
* a new, independent, API and plugin abstraction for prompting the user, generating said dictionary, etc

Now, the CredUI implementation above is very OS X-specific, but one could certainly generalise the interaction with GSS-API (which would mostly come down to defining a GSS-API dictionary type, accessors, and well known keys).

-- Luke