I don't know if something changed. I tried login to armory with PHP today (using PEAR) and I was successful. I had one issue - maybe you have similar. After I POSTed login data to server, when I tried to GET auction house page, I was not logged in. The trick was, that you have to GET the AH page (or any other page) with ST parameter stored in cookies as BA-tassadar.

Details:
Set-Cookie: BA-tassadar=EU-111111-aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa; Domain=battle.net; Expires=Wed, 20-Apr-2011 19:31:22 GMT; Path=/login; Secure
Set-Cookie: login.key=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa; Domain=battle.net; Expires=Wed, 20-Apr-2011 19:31:22 GMT; Path=/
Set-Cookie: cl=aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa; Domain=battle.net; Path=/login; Secure

The GET page like:
https://eu.battle.net/wow/en/vault/c...aaaaaaaaaaaaaa

And that's it :)

If you have further questions, let me know.