Getting php session variables frojavascript form

[facarroll]

I'm totally new to javascript and fairly new to php... so...
I have a javascript login form that takes a users email and password, validates through a mysql database and gains entry to a folder that is protected by a htaccess file. This is set up to integrate with a PayPal subscription.
All OK so far.
The problem I have is that the folder contains several php files that require session data. Can anyone tell me if there is a way that the user email and password entered into the javascript form can be used as a hidden login for the php files. I want to avoid a second login for obvious reasons.

The javascript is below. I don't have a problem with making a php login work from a form, but how can I hide the form and use the javascript data?

window.onload = function()
{
    var anchors = document.getElementsByTagName("a");
    for (var foo = 0; foo < anchors.length; foo++) {
        if (anchors[foo].className == "httpauth") {
			
			if ( (BrowserDetect.browser != 'Safari') && (BrowserDetect.browser != 'Opera') )  {			
	            createForm(anchors[foo]);			
			}
			
        }
    }
}

function createForm(httpauth)
{
    var form = document.createElement("form");
    form.action = httpauth.href;
    form.method = "get";
    form.onsubmit = login;
    form.id = httpauth.id;
	
    var username = document.createElement("label");
    var usernameInput = document.createElement("input");
    usernameInput.name = "username";
    usernameInput.type = "text";
    usernameInput.id = httpauth.id + "-username";
    username.appendChild(document.createTextNode("Username : "));
    username.appendChild(usernameInput);
	
    var password = document.createElement("label");
    var passwordInput = document.createElement("input");
    passwordInput.name = "password";
    passwordInput.type = "password";
    passwordInput.id = httpauth.id + "-password";
    password.appendChild(document.createTextNode("Password : "));
    password.appendChild(passwordInput);

	var submit = document.createElement("input");
    submit.type = "submit";
    submit.value = "Log in";
	
    form.appendChild(username);
    form.appendChild(password);
    form.appendChild(submit);

	var logoutLink = document.createElement("a");
    /*logoutLink.href = "#";
    logoutLink.onclick = logout;
    logoutLink.appendChild(document.createTextNode("Log out"));
    form.appendChild(logoutLink);*/
    httpauth.parentNode.replaceChild(form, httpauth);
}

function getHTTPObject() {
	var xmlhttp = false;
	if (typeof XMLHttpRequest != 'undefined') {
		try {
			xmlhttp = new XMLHttpRequest();
		} catch (e) {
			xmlhttp = false;
		}
	} else {
        /*@cc_on
        @if (@_jscript_version >= 5)
            try {
                xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
            } catch (e) {
                try {
                    xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
                } catch (E) {
                    xmlhttp = false;
                }
            }
        @end @*/
    }
	return xmlhttp;
}

function login()
{
    var username = document.getElementById(this.id + "-username").value;
    var password = document.getElementById(this.id + "-password").value;
    var http = getHTTPObject();
	//var url = "http://" + username + ":" + password + "@" + this.action.substr(7);
	var url = this.action;
    http.open("get", url, false, username, password);
    http.send("");
	if (http.status == 200) {
		document.location = url;
	} else {
        alert("Incorrect username and/or password!");
    }
    return false;
}

function logout()
{
    var http = getHTTPObject();
    http.open("get", this.parentNode.action, false, "null", "null");
    http.send("");
    alert("You have been logged out.");
    return false;
}

//http://www.quirksmode.org/js/detect.html
var BrowserDetect = {
	init: function () {
		this.browser = this.searchString(this.dataBrowser) || "An unknown browser";
		this.version = this.searchVersion(navigator.userAgent)
			|| this.searchVersion(navigator.appVersion)
			|| "an unknown version";
		this.OS = this.searchString(this.dataOS) || "an unknown OS";
	},
	searchString: function (data) {
		for (var i=0;i<data.length;i++)	{
			var dataString = data[i].string;
			var dataProp = data[i].prop;
			this.versionSearchString = data[i].versionSearch || data[i].identity;
			if (dataString) {
				if (dataString.indexOf(data[i].subString) != -1)
					return data[i].identity;
			}
			else if (dataProp)
				return data[i].identity;
		}
	},
	searchVersion: function (dataString) {
		var index = dataString.indexOf(this.versionSearchString);
		if (index == -1) return;
		return parseFloat(dataString.substring(index+this.versionSearchString.length+1));
	},
	dataBrowser: [
		{ 	string: navigator.userAgent,
			subString: "OmniWeb",
			versionSearch: "OmniWeb/",
			identity: "OmniWeb"
		},
		{
			string: navigator.vendor,
			subString: "Apple",
			identity: "Safari"
		},
		{
			prop: window.opera,
			identity: "Opera"
		},
		{
			string: navigator.vendor,
			subString: "iCab",
			identity: "iCab"
		},
		{
			string: navigator.vendor,
			subString: "KDE",
			identity: "Konqueror"
		},
		{
			string: navigator.userAgent,
			subString: "Firefox",
			identity: "Firefox"
		},
		{
			string: navigator.vendor,
			subString: "Camino",
			identity: "Camino"
		},
		{		// for newer Netscapes (6+)
			string: navigator.userAgent,
			subString: "Netscape",
			identity: "Netscape"
		},
		{
			string: navigator.userAgent,
			subString: "MSIE",
			identity: "Explorer",
			versionSearch: "MSIE"
		},
		{
			string: navigator.userAgent,
			subString: "Gecko",
			identity: "Mozilla",
			versionSearch: "rv"
		},
		{ 		// for older Netscapes (4-)
			string: navigator.userAgent,
			subString: "Mozilla",
			identity: "Netscape",
			versionSearch: "Mozilla"
		}
	],
	dataOS : [
		{
			string: navigator.platform,
			subString: "Win",
			identity: "Windows"
		},
		{
			string: navigator.platform,
			subString: "Mac",
			identity: "Mac"
		},
		{
			string: navigator.platform,
			subString: "Linux",
			identity: "Linux"
		}
	]

};
BrowserDetect.init();