A post on the Squeak mailing list made me reevaluate how difficult it would be to add NTLM and SPNEGO support to WebClient. Since I had done this at work before (via a plugin interface to support both Windows and Mac transparently) I figured it would be straightforward to implement it using the Squeak FFI interface. And indeed it is. The code is pretty small and a reasonable example on how to use the FFI to access the Microsoft SSP interface.
Using code someone else is already maintaining is a good idea. I've done Digest Auth and the xAuth piece of OAuth myself, and let me tell you - specs are written in a strange language, even though all of the words are English :)