Multiple KDC's realm heuristic for KRB5CCNAME=DIR:/tmp/mydir/ ccache not working
ghudson at mit.edu
Tue Jul 24 14:47:38 EDT 2018
On 07/24/2018 01:56 PM, Martin Gee wrote:
> Added: krbdev at mit.edu
Please pick one list or the other. I've left the message to
kerberos at mit.edu in the moderation queue and omitted it from the to line
> 2. If the realm of the target service is known via a [domain_realm]
> mapping in krb5.conf, a client principal in that realm will be selected.
> Do the mechanisms you list work for constrained delegation?
They do not.
Constrained delegation (S4U2Proxy) requires an evidence ticket. MIT's
library supports two ways of getting an evidence ticket: either by using
protocol transition (S4U2Self) via a call to
gss_acquire_cred_impersonate_name(), or by receiving the evidence ticket
from a Kerberos-using client via gss_accept_sec_context().
In the first case (which is what t_s4u does),
gss_acquire_cred_impersonate_name() has no idea what the constrained
delegation target server will be, so it has to resolve the
impersonator_cred_handle with no target name, which means picking the
primary cache. The TGT from that same cache will be used for the
constrained delegation step.
In the second case, gss_accept_sec_context() constructs an evidence cred
containing the TGT from the verifier cred handle and the ticket
presented by the client. Again, gss_accept_sec_context() has no idea
what the constrained delegation target server will be, so it picks the
TGT from the primary cache. This could possibly be improved by looking
for a TGT which matches the server key the client authenticated to, but
that is not implemented.
To make S4U2Self+S4U2Proxy work with credential cache selection, I think
we would need a way to do it in one step. I can't think of an easy way
to express that with current GSS function signatures.
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