app.js

var authorization_grant = 'CAAHn34BO0R0BABtJyxdrZCQzakdmgJZBoQa0U...'; //saved from previous step
var xhr = Titanium.Network.createHTTPClient();
xhr.setTimeout(30000);
xhr.onload=function() {
    Ti.API.info('access_token: '+JSON.parse(this.responseText).authenticationToken); // save this for requesting protected resource
};
xhr.onerror= function() {
    Ti.API.info('Auth Failure response: '+this.responseText);
};
xhr.open('POST', 'https://my_resource_auth_server.azure-mobile.net/login/facebook');
xhr.setRequestHeader("Content-Type", "application/json");
xhr.setRequestHeader("Accept", "application/json");
xhr.send({
    "access_token" : authorization_grant
});