Nathan Kinder wrote:
On 12/06/2009 02:03 PM, Alexey Melnikov wrote:
Nathan Kinder wrote:
Hi,
Hi Nathan,
I'm a developer working on an LDAP server application (389 Directory
Server) that uses Cyrus
SASL. We've been using Cyrus SASL successfully for quite some time,
but I have an odd issue I'm
seeing trying to use the digest-md5 mechanism with multiple realms.
The problem is that a realm set by the client (Mozilla ldapsearch or
OpenLDAP ldapsearch in this
case) never appears to be sent to the server. I would like to use
the client specified realm in
my SASL_CB_CANON_USER callback to allow the server to locate the
appropriate entry that contains
the shared secret.
I looked through the Cyrus SASL code, and the root of the problem
looks to be that there is no
way to set multiple realms when calling sasl_server_new(). The
user_realm parameter is just a
single "char *", which is just used as is by the call to
add_to_challenge() in the
digestmd5_server_mech_step1() function. I see no logic here to add
multiple realms to the
challenge that is sent to the client.
Right.
The client side of the digest-md5 plug-in has logic to handle
multiple realms. The
ask_user_info() function deals with this by looking for any realms
that were in the challenge.
If no realm was found, it fakes it by using the FQDN of the server.
If a single realm is found,
the client just uses it. If multiple realms are found, then it
appears an interaction is used,
meaning the client specified realm will be set. Since only one
available realm is sent in the
challenge from the server, the client specified realm will never be
used.
Correct.
Is my above interpretation of the code correct, or am I missing
something? Should it be
possible to set multiple available realms on the server side and
have them passed to the
client in the challenge?
Are you sure you actually need support for multiple realms as opposed
to just using usernames in the form of "user@domain"?
I don't have a strong need for this as it was simply an issue that
came up during testing of our code for mapping an authcid to an LDAP
entry. I noticed that a realm set on the client side (ldapsearch) was
never passed to the server, and my investigation led to the above.
RFC 2831 led me to believe that multiple realms should be possible.
Right.
If you are, then the code can be extended to handle what you want,
but that wouldn't be entirely trivial and this change will be quite
specific to DIGEST-MD5 plugin.
I think it would be nice to have eventually, but I understand that it
is not a trivial issue to fix (particularly without changing the API).
Yes, I think this would require changing APIs, adding a new callback or
similar.
Are there other mechanisms that allow multiple realms that would
benefit from this as well (such as CRAM-MD5), or does this truly only
affect DIGEST-MD5?
There is no other SASL mechanism I know of that uses realms in the same way.
