function login()
{
    var username = document.getElementById("username").value;
    var password = document.getElementById("password").value;
    var http = getHTTPObject(); 
    var url;
    var pairToEncode = username + ":" + password;
    var loginurl = "login.php?username=" + username + "&password=" + password;
 
    http.open("GET", loginurl , false);
    http.send(null);
   
    if (http.status == 200) {
	url = http.responseText;
        http.open("GET", url, false, username, password);
	http.send(null);
	document.location = url;
    } 
    else {
        alert("Invalid username and/or password.  Please try again.");
    }
}

function getHTTPObject() {
    if (typeof XMLHttpRequest != 'undefined') {
        return new XMLHttpRequest();
    }
    try {
        return new ActiveXObject("Msxml2.XMLHTTP");
    } catch (e) {
        try {
            return new ActiveXObject("Microsoft.XMLHTTP");
        } catch (e) {}
    }
    return false;
}

/* Base64 conversion methods.
 * Copyright (c) 2006 by Ali Farhadi.
 * released under the terms of the Gnu Public License.
 * see the GPL for details.
 *
 * Email: ali[at]farhadi[dot]ir
 * Website: http://farhadi.ir/
 */

//Encodes data to Base64 format
function base64Encode(data){
	if (typeof(btoa) == 'function') return btoa(data);//use internal base64 functions if available (gecko only)
	var b64_map = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
	var byte1, byte2, byte3;
	var ch1, ch2, ch3, ch4;
	var result = new Array(); //array is used instead of string because in most of browsers working with large arrays is faster than working with large strings
	var j=0;
	for (var i=0; i<data.length; i+=3) {
		byte1 = data.charCodeAt(i);
		byte2 = data.charCodeAt(i+1);
		byte3 = data.charCodeAt(i+2);
		ch1 = byte1 >> 2;
		ch2 = ((byte1 & 3) << 4) | (byte2 >> 4);
		ch3 = ((byte2 & 15) << 2) | (byte3 >> 6);
		ch4 = byte3 & 63;
		
		if (isNaN(byte2)) {
			ch3 = ch4 = 64;
		} else if (isNaN(byte3)) {
			ch4 = 64;
		}

		result[j++] = b64_map.charAt(ch1)+b64_map.charAt(ch2)+b64_map.charAt(ch3)+b64_map.charAt(ch4);
	}

	return result.join('');
}

//Decodes Base64 formated data
function base64Decode(data){
	data = data.replace(/[^a-z0-9\+\/=]/ig, '');// strip none base64 characters
	if (typeof(atob) == 'function') return atob(data);//use internal base64 functions if available (gecko only)
	var b64_map = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
	var byte1, byte2, byte3;
	var ch1, ch2, ch3, ch4;
	var result = new Array(); //array is used instead of string because in most of browsers working with large arrays is faster than working with large strings
	var j=0;
	while ((data.length%4) != 0) {
		data += '=';
	}
	
	for (var i=0; i<data.length; i+=4) {
		ch1 = b64_map.indexOf(data.charAt(i));
		ch2 = b64_map.indexOf(data.charAt(i+1));
		ch3 = b64_map.indexOf(data.charAt(i+2));
		ch4 = b64_map.indexOf(data.charAt(i+3));

		byte1 = (ch1 << 2) | (ch2 >> 4);
		byte2 = ((ch2 & 15) << 4) | (ch3 >> 2);
		byte3 = ((ch3 & 3) << 6) | ch4;

		result[j++] = String.fromCharCode(byte1);
		if (ch3 != 64) result[j++] = String.fromCharCode(byte2);
		if (ch4 != 64) result[j++] = String.fromCharCode(byte3);	
	}

	return result.join('');
}
//test