How do I get my Applet to access a password protected page?

There are two ways to do have your applet access a password protected page. The first does not involve any Java code; the second is a pure Java solution.

Since Netscape caches the username and the password, you can let Netscape do the authentication for you. It automatically be done if the following conditions are met:

Assuming that you are using the basic authentication scheme, the applet includes the http authorization header itself. The value of the header should be a BASIC authentication-string where the authentication-string is a base64 encoding with the form user:password.

In Sun's commerce API, there is a Base64 encoder class: javax.commerce.util.BASE64Encoder. Here, you can either use that encoder class or write one yourself. (All the information you need is found in RFC 1521). To ensure that the browser actually sets the header, some output has to be sent to the server (i.e., the request must be a POST request):
String userid;
String password;
URL cgiURL;
...
try {
URLConnection con = cgiURL.openConnection();
con.setDoInput(true);
con.setDoOutput(true);
con.setRequestProperty(("Authorization", MYBase64Encoder.encode(userid + ":" + password");
con.getOutputStream().close()
//We make a POST request even if we do not send data
InputStream in = con.getInputStream()//Continue as normal
} catch(IOException ioexc){
// Can mean that we did not supply a valid user-password pair
}