[c#] Read Post Data submitted to ASP.Net Form

I have a working login form in an asp.net application. Standard stuff with a username and password text box and a button to process the login. Works fine.

I have a new requirement to allow the user to input the username and password from a separate plain html page that is not a part of my asp.net application. I plan on achieving this using standard html - form, input, submit button etc. The form action will be the URL of my asp.net login page and its method will be POST.

What I want to do in the C# code behind page of the asp.net login form, presumably in the Page_Load event, is to check if the request for the page contains a username and password value being passed in. If it does then I need to read those values and process the login as if someone had clicked the login button on the asp.net page. If not then I will display the login form as usual.

How do I check for the existence of, and read, the username and password values in the request for my page.

NameValueCollection nvclc = Request.Form;
string   uName= nvclc ["txtUserName"];
string   pswod= nvclc ["txtPassword"];
//try login
CheckLogin(uName, pswod);

if (!string.IsNullOrEmpty(Request.Form["username"])) { ... }

username is the name of the input on the submitting page. The password can be obtained the same way. If its not null or empty, it exists, then log in the user (I don't recall the exact steps for ASP.NET Membership, assuming that's what you're using).