[OpenAFS-devel] token passing in modern ssh?

[Jeffrey Altman]

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Jim Rees wrote:
>   I am very confused by this statement.  In what way does MIT prevent you 
>   from obtaining TGTs in multiple realms?
> 
> Of course it's possible.  What I said was that MIT didn't think it would be
> useful.  If they had, they would have provided an api, or allowed multiple
> tgts in a single cache.

Interesting statement and quite unfair.

The MIT Kerberos team does as much as it can do with its limited 
resources.  There is certainly an understanding that the CCAPI and its 
support for multiple principals are important.  There is also an 
understanding that a high level library for managing multiple principals 
is necessary.  The Macintosh has both the functionality and the Kerberos 
Logon Library API.

Unfortunately, we also understand that other things such as thread 
safety, incremental database propagation, plug-in architectures, pkinit,
GSS-API changes to support UMich's NFSv4 implementation, etc. are also 
important and in many cases more so.

As I have said in a previous response to this thread.  The debate over
the technical reasons why credential caches only contain a single 
principal have been held on krbdev@mit.edu.  If you want to discuss this 
matter further, the appropriate place to do so is in that forum.  Not 
one focused on OpenAFS.  Not all of the parties who need to be in such
as discussion monitor this list.


>   OpenAFS for Windows manages multiple credential caches.  If you want 
>   this functionality in OpenSSH, consider writing a patch.
> 
> I fail to see how this helps.

Your issue is that you want to provide the ability to identify multiple
credential caches in the OpenSSH client, forward credentials from them
to the server, and allow the server to use the forwarded TGTs to obtain
service tickets for various cells.

It occurred to me that C-Kermit has had this functionality for several
years.  What you need to do is provide an extension to OpenSSH which
specifies the list of credential cache files from which you would like
to forward credentials.  The SSH protocol may need to be extended to
support the forwarding of multiple KERB_CRED messages to the server.
Assuming that is possible the client will examine each credential cache,
obtain the default principal name and forward a TGT to the sshd.
The sshd would in turn accept the KERB_CRED, determine which principal 
it is for and then look up in a mapping table for the user the list of 
cells for which afs service tickets should be obtained using that 
principal.  The sshd can also produce multiple credential caches to 
store the forwarded TGTs as appropriate.  You will then need to
export the list to the environment in some manner.  On krbdev@mit.edu
we have previously discussed extended KRB5CCNAME to be a list of
krb5_ccache names.  However, we are concerned about backwards 
compatibility.

When the CCAPI is used this is not an issue because the CCAPI itself
can be used to query a list of credential caches.

Jeffrey Altman

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