[mod_python] AttributeError: 'mp_request' object has no attribute 'ssl_var_lookup'

I'm migrating a functioning mod_python handler from Windows (Apache 2.0.63, Python 2.3) to
CentOS 5.1 (Apache 2.2.3, Python 2.4) and am getting a very strange error:

Mod_python error: "PythonFixupHandler myHandler"
Traceback (most recent call last):
  File "/usr/lib/python2.4/site-packages/mod_python/apache.py", line 299, in HandlerDispatch
    result = object(req)

  File "/var/www/mypy/myHandler.py", line 16, in fixuphandler
    ssl_client_dn = req.ssl_var_lookup('SSL_CLIENT_S_DN')

AttributeError: 'mp_request' object has no attribute 'ssl_var_lookup'

I've been searching all afternoon and my Google-fu has failed me.  I haven't been able to determine
why on the CentOS platform the request object suddenly has no ssl_var_lookup attribute.

Any help would be appreciated,

Thanks,
Rich