Security Thingie

You know that dialog box that appears when you try to connect to a paswworded page and it asks you for a username and password and has the domain name on it ?

Well im making a web server and want to know how to re-create that box by sending the html code to the user.

Does anyone know how to do this ?

This is a complete description of the http: http://www.ietf.org/rfc/rfc1945.txt It also contains the security info, search the file for "password".

Thankyou, thats very useful.