I'm developing a javascript App that needs, as part of its functionality, for users to be able to update their Twitter status. The App is designed to work on mobiles, and as such I don't really want to be sending users all the way over to the Twitter site to sign in; they should just be able to pass their credentials to the app, and I'll handle all the signin. So I'm trying to use the Basic Auth with the restful API. My code looks like: function postTweet(input){ $.ajax( { type: "POST", url: "http://twitter.com/statuses/update.json", data: {status: input}, dataType: "json", error: function() { alert("Some error occured"); }, success: function() { alert("Success!"); }, beforeSend: function(request) { request.setRequestHeader("Authorization", "Basic BASE64OFMYCREDENTIALS");} } ) ; } So, as far as I'm aware, this should perform the authentication from the XMLHttpRequest header, and then post the status. However, whenever I call this code, I get a "401 Unauthorized" error from Twitter. Below are the request & response headers from firebug: Request: OPTIONS /statuses/update.json HTTP/1.1 Host: twitter.com User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9.2) Gecko/20100115 Firefox/3.6 Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 Accept-Language: en-gb,en;q=0.5 Accept-Encoding: gzip,deflate Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive: 115 Connection: keep-alive Origin: null Access-Control-Request-Method: POST Access-Control-Request-Headers: authorization Response: HTTP/1.1 401 Unauthorized Date: Sat, 13 Mar 2010 11:08:58 GMT Server: hi Status: 401 Unauthorized WWW-Authenticate: Basic realm="Twitter API" X-Runtime: 0.00204 Content-Type: application/json; charset=utf-8 Cache-Control: no-cache, max-age=300 Set-Cookie: guest_id=1268478538488; path=/ _twitter_sess=BAh7CDoPY3JlYXRlZF9hdGwrCPlyNlcnAToHaWQiJWUyN2YzYjc3OTk2NGQ3%250ANzJkYTA4MjYzOWJmYTQyYmUyIgpmbGFzaElDOidBY3Rpb25Db250cm9sbGVy%250AOjpGbGFzaDo6Rmxhc2hIYXNoewAGOgpAdXNlZHsA--d687808459872da0aa6a89cab35fd347300b4d07; domain=.twitter.com; path=/ Expires: Sat, 13 Mar 2010 11:13:58 GMT Vary: Accept-Encoding Content-Encoding: gzip Content-Length: 88 Connection: close Any help with this would be much appreciated, Thanks, jelford ps. I should mention I'm using JQuery, incase it's not clear.