FMS server user authentication

You can pass variables to the SWF like you are already doing with "serverName" and "skinName" etc. Just pass "app_username=joe" and "app_password=test" and you can read those variables inside your swf and pass them in the netconnection.connect() method like this:

swf code:
my_netconnection.connect("rtmp://myserver.com/my_application/my_instance",my_parameter1, my_parameter2, etc);

(you can pass as many parameters as you want on the .connect line)

But to make things a bit more flexibel I would put all parameters inside an object and pass the object so your .connect method is a bit more readable:

swf code:
obj_parameters = new Object();
obj_parameters.login = app_loginname; // you got this from outside the swf
obj_parameters.password = app_password; // you got this from outside the swf
obj_parameters.my_integer = 726262; // example
obj_parameters.my_name = "guess what, a demo";

my_nc = new Netconnection();
my_ncconnect("rtmp://myserver.com/my_application/my_instance", obj_parameters);

server code:

application.onConnect = function (obj_client, obj_client_parameters) {
// obj_client is always submitted
// obj_client_parameters holds your parameters
client_login = obj_client_parameters.login;
client_password = obj_client_parameters.password;
// now go and start and XML object and supply login + password as parameters like this:

my_xml = new XML();
my_xml.onLoad = function() {
// check the result;
}
my_xml.load("url?login=" + client_login + "&password=" + client_password);
// call the script and supply the login & password the client submitted
// let the script verify the combination
// return a true or false
// accept the users connection or kill it
}

etc