post to twitter from my own website

In my web site, I have a text message and I want to post it in my own twitter by pushing a submit button. It works if I already logged in to my twitter from twitter website but if I don't, it goes to login page and after logging in, it posted the message.

My code is:

(in my form)

   <cftextarea name="Twittermsg"  tooltip="Twitter message" id="Twittermsg" style="width:530px" />
   <cfinput type="button" name="btn1" id="btn1" onClick="pushbtn();" />

(javascript)

<script type="text/javascript" >

function pushbtn(){
var var1=document.getElementById("Twittermsg").value;

var twtLink = 'http://twitter.com/home?status='+encodeURIComponent(var1);
window.open(twtLink) ;
}

</script>

Can anyone help me to write code for automatically log in to my own web page?

Thanks,

Mandana