Alternative proxy-creds API for constrained-delegation

[Isaac Boukris]

On Wed, Jun 3, 2020 at 6:53 AM Nico Williams <nico at cryptonector.com> wrote:
>
> On Tue, Jun 02, 2020 at 10:30:47PM -0500, Nico Williams wrote:
> > On Wed, Jun 03, 2020 at 01:29:23AM +0200, Isaac Boukris wrote:
> > > On Wed, Jun 3, 2020 at 12:05 AM Nico Williams <nico at cryptonector.com> wrote:
> > > > On Tue, Jun 02, 2020 at 08:35:14PM +0200, Isaac Boukris wrote:
> > > > > I'd still love to see an application signal for the service ticket
> > > > > using a cred option or name attribute, more likely to help in samba.
> > > >
> > > > What exactly would the option specify?  I'm certain we can fit it in one
> > > > of three different ways though.
> > >
> > > It could specify the delegation-policy for this creds/context for
> > > example, or we can make the ticket always available via
> > > name-attributes like Simo suggested, but that would be somewhat
> > > unrelated work.
> >
> > So you're saying you want to be able to say "only accept traditional
> > delegated credentials, don't do S4U2Proxy" and also be able to say
> > "either is fine"?  And configuration is not enough?  Anyways, my
> > preference for that is to use gss_acquire_cred_from().
>
> I'll take that back!  The right interface for this is
> gss_store_cred_into() or gss_store_cred_into2().
>
> Here's the idea:
>
>  - you always get a deleg_cred_handle if one was delegated or S4U2Proxy
>    is available,
>
>  - you tell gss_store_cred_into() about what you're willing to store and
>    with what options,
>
>  - if you say "only real creds" then gss_store_cred_into() will not
>    store S4U2Proxy creds.

This sounds a lot of application logic, and we also don't want to
implicitly delegate a ticket at this point.

btw, we don't have to call it s4u2proxy creds, it's just a tgt-less
cache with a service ticket, maybe we could use it in different
manners as well (for local auth, or maybe invent a way to authenticate
to the kdc with it?).