Steam Post Request - Failed to load resource: the server responded with a status of 400 (Bad Request)

Question

I'm trying to send a post request like this:

xhr.open("POST", "/steamapi/actions/RemoveFriendAjax", false);
    var params = "sessionID="+session_id+"&steamid="+id;
    xhr.onreadystatechange = function() {//Call a function when the state changes.
        if(xhr.readyState == 4 && xhr.status == 200) {
            alert(xhr.responseText);
        }
    }   
xhr.send(params);

I'm using an Apache Server, and this is my .htaccess file

RewriteEngine On
RewriteRule ^api/(.*)$ http://api.steampowered.com/$1 [P]
RewriteRule ^(.*)$ http://steamcommunity.com/$1 [P]
 <IfModule mod_headers.c>
    Header add Access-Control-Allow-Origin "*"
    Header add Access-Control-Allow-Headers "origin, x-requested-with, content-type"
    Header add Access-Control-Allow-Methods "PUT, GET, POST, DELETE, OPTIONS"
 </IfModule>

Whenever I send the request I get this error:

Failed to load resource: the server responded with a status of 400 (Bad Request) 
enter code here

Why is this happening? I have used GET requests with Steam and they work fine, put this POST request doesn't seem to be working.

EDIT: This is steamcommunity.com's robot.txt file:

User-agent: *
Disallow: /actions/
Disallow: /linkfilter/
Host: steamcommunity.com

It says Disallow: /actions/ , so is this the reason why I'm getting a 400 error?

Answer 1

Did you use setRequestHeader ?

xhr.open("POST", "/steamapi/actions/RemoveFriendAjax", false);
xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");