GSSAPI server side on Linux, SSPI client side on Windows

Hello again!

I've been setting up my PostgreSQL server by doing something I've
never done before: I've joined a Linux server to a domain so I can use
integrated Kerberos authentication from server to server.

I've managed to make this work from Linux machine to Linux machine. On
the client, I retrieve my Kerberos ticket with kinit, and then I can
use psql with my username to connect to the server without a password
over GSSAPI. So far, so good.

However, the eventual goal was to connect to this same server from a
.NET app running on Windows, and here I've run into a snag. The Npgsql
library does not support GSSAPI—it only supports SSPI, which is
nearly-but-not-enough-like the same thing to count in this situation,
because I can't seem to configure my PostgreSQL on Linux to accept
SSPI. If I try it, I get the error:

invalid authentication method "sspi": not supported by this build

The docs say that SSPI is supported if GSSAPI is available
(http://www.postgresql.org/docs/9.3/static/auth-methods.html#SSPI-AUTH)
Is this just a matter of me running the wrong build? I'm using
PostgreSQL 9.3 from the official builds for Debian 6.

If the docs are wrong, and SSPI isn't available server-side on Linux,
what are my other options?

—Brian