gssproxy: Don't refresh expired delegated credentials
`mod_auth_gssapi` exports delegated credentials into `/run/ipa/ccaches`
and pass down that path as `KRB5CCNAME` env variable to WSGI worker.
GSSProxy in turn, protects these credentials from direct usage of
`ipa-api`. But the configuration of `service/ipa-api` (in particular,
'cred_store = client_keytab:/var/lib/ipa/gssproxy/http.keytab') and
default GSS name ('=None') dictates to refresh expired credentials
with the client's keytab overwriting the origin credentials with
initial credentials of keytab's principal.
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>