Why does oauth signature and token fail when validating?

var URL = 'https://api.twitter.com/oauth/request_token';
var parameters = {
        oauth_consumer_key : 'key',
        oauth_nonce : 'kllo9940pd9333jh',
        oauth_timestamp : '1191242096',
        oauth_signature_method : 'HMAC-SHA1',
        oauth_version : '1.0',
};

var consumerSecret = 'key';
var encodedSignature =  oauthSignature.generate('POST', URL, parameters, consumerSecret);
var callback = encodeURIComponent('127.0.0.1:3000');
var consumerkey = encodeURIComponent('key');
var oauthNonce = encodeURIComponent('kllo9940pd9333jh');

App.TwitterController = Ember.ObjectController.extend({

    actions: {  

        loginTwitter: function() {
            console.log('Event Clicked');
            console.log(parameters);
            console.log(encodedSignature);
            console.log(URL);
            console.log(consumerSecret);
            console.log(callback);
            console.log(oauthNonce);
            return new Ember.RSVP.Promise(function(resolve, reject) {
            Ember.$.ajax({
                url:         'https://api.twitter.com/oauth/request_token',
                type:        'POST',
                contentType: "json",
                headers: {
                    "Authorization": 'OAuth oauth_callback='+ callback +', oauth_consumer_key='+ consumerkey +', oauth_nonce='+ oauthNonce +', oauth_signature='+ encodedSignature +', oauth_signature_method="HMAC-SHA1", oauth_timestamp="1191242096", oauth_version="1.0"'
                },

                contentType: 'application/x-www-form-urlencoded'
            }).then(function(response) {
                console.log('Successed');
                console.log(response);
                resolve (response);
            }, function(xhr, status, error) {
                console.log(error);
                console.log('In Error');
                reject(error);
            });
        });
        },
    }
});

I above code is for request token from the twiiter but it give error Failed to validate oauth signature and token error occur. How I resolve this? Why this happen?

Is there problem in my oauth_signature my oauth_signature is j%2BkemjnrvI2%2BBERPE7hf6bTb7Ds%3D.