Access Control with VMailMgr's checkvpw / Dan Bernstein's checkpassword

[Daniel Lorch <ml-daniel@lorch.cc>]

hi,

I am trying to set up OpenLDAP with an external authentication mechanism
that conforms to DJB's 'checkpassword' interface:

  http://cr.yp.to/checkpwd/interface.html

The checkpassword is summarized very quickly: It takes a username and password
each delimited by \0 and gives a return code for success or failure. In
particular I am trying to interface 'checkvpw' which comes with VMailMgr:

  http://www.vmailmgr.org/docs/checkvpw.html

VMailMgr is a piece of software, that allows having virtual users with
individual passwords on every domain and is therefore extremely attractive
for mass virtual hosting.

My ultimate goal would be to have OpenLDAP authenticate against 'checkvpw'
in order to allow every virtual user having access to their own subtree.
Every virtual user would then be given the ability to store their address
book in LDAP, which could be interfaced by both mail clients and webmail,
which would be IMP in conjunction with Turba:

  http://www.horde.org/imp/
  http://www.horde.org/turba/

Has anyone already successfully authenticated against 'checkvpw' or is
there a _simple method_ of accessing an external authentication mechanism?
I know there is SASL, but that would involve heavy development and I'd
like to avoid that if possible :) Any help or hints would be greatly
appreciated.

-daniel