MongoDB 2.4 will support SASL authentication in its enterprise build. The initial implementation is intended to support GSSAPI. PyMongo will initially support this using pykerberos:

http://pypi.python.org/pypi/kerberos (specifically kerberos-1.1.1 or newer)

For documentation download the tarball (http://pypi.python.org/packages/source/k/kerberos/kerberos-1.1.1.tar.gz) and read the source. None of the versions at http://trac.calendarserver.org/browser/PyKerberos match the tarball on pypi.

This limits support to Python 2.x for the time being. Future releases may shift to a different library (possibly home grown at 10gen) to support SASL authentication methods (CRAM-MD5, DIGEST-MD5, etc.) and other Python interpreter versions.