BUG #5895: Ability to match more than just CN in client certificate

The following bug has been logged online:

Bug reference: 5895
Logged by: Christopher Head
Email address: chris2k01(at)hotmail(dot)com
PostgreSQL version: 9.0.3
Operating system: Linux amd64
Description: Ability to match more than just CN in client certificate
Details:

This is a feature request/wishlist, not a bug. Right now, when using client
certificates over SSL for authentication, the username map maps from the
Subject Common Name field in the certificate to a username in the database.
It would be nice if matches could be done on a few other fields in the
certificate. For example, my name is not particularly unusual, so it's
reasonable that someone else in the world might (and probably does) have the
same name. That doesn't mean I want to give that person access to my
database, even if they also get a certificate from e.g. cacert.org!

A few fields to match on that would pretty much instantly close this hole
would be e-mail address and certificate serial number. While the e-mail
address suggestion could be generalized to match an arbitrary subset of the
subject's distinguished name fields (e.g. write something like
/O=FooOrg/CN=Christopher Head/ to require that both fields must be present
with the specified values), matching certificate serial number would be
slightly different as the serial number is not part of the distinguished
name. It would probably be the most secure field to match on, however, as no
CA will ever issue two certificates with the same serial number. E-mail
address would be a close second as an address can only be held by one
person, though it relies on the CA being able to verify the legitimate owner
of the address.