visionmedia/superagent — pull request #199 by MatthewMueller (2013-04-02 10:39:39+00:00)
Title: Added client-side basic auth

Same signature as node's version: `.auth(user, pass)`

One caveat is that base64 encoding (`btoa`) is not well supported in IE. It'd be easy to support with something like: https://github.com/ForbesLindesay/base64-encode, but I'm not sure what you think of an additional dependency.