[krbdev.mit.edu #9029] gss_acquire_cred_from() and gss_krb5_ccache_name() collection behavior

Sun Sep 12 12:11:36 2021: Request 9029 was acted upon.
 Transaction: Ticket created by [email protected]
       Queue: krb5
     Subject: gss_acquire_cred_from() and gss_krb5_ccache_name() collection
 behavior
       Owner: Nobody
  Requestors: [email protected]
      Status: new
 Ticket <URL: http://kerborg-prod-app-1.mit.edu/rt/Ticket/Display.html?id=9029 >


Ticket 8010 changes the behavior of gss_store_cred() and gss_store_cred_into()
to use kinit-like logic to pick a ccache when presented with a collection
name, regardless of whether the ccache name is presented via a cred store,
gss_krb5_ccache_name(), or the default ccname.

gss_acquire_cred() has used collection logic since ticket 6958 if it uses the
default ccname.  But if it is given a ccache collection name via a cred store
or gss_krb5_ccache_name() call, it immediately resolves the given name and
therefore uses only the collection's primary cache.

Before changing this behavior we should consider the ramifications for
behavior Windows (where gss_store_cred() applications are probably unusual but
gss_acquire_cred() applications aren't).  While on Unix-like platforms we have
migrated towards collection contents being dictated entirely by the default
ccname, Windows still presents a collection containing the LSA cache and all
API caches.  Therefore, if we simply set the context default ccname to the
caller-provided ccache name, on Windows we might still select a cache from an
entirely different ccache type.

There are basically four options:

1. Leave gss_acquire_cred() alone (i.e. continue to treat a caller-specified
ccache name as determining a single cache, not a collection).

2. Change gss_acquire_cred() to use collection semantics for a
caller-specified ccache name and ignore potential problems on Windows.

3. Bring Windows ccache collection behavior in line with the Unix-like
platforms, and modify Leash to explicitly enumerate the LSA and API caches
rather than rely on finding them via the ccache collection.

4. Add a new collection API for krb5_cc_cache_match() with an added ccname
parameter (as described in https://k5wiki.kerberos.org/wiki/Projects/
Credential_cache_collection_improvements#New_collection_architecture ) and use
it for acquire_cred cache selection.  Ensure that the new API only enumerates
the designated collection when one is specified.