How can I use HTTP authorization in my program?

Question

I'm writing full-featured proxy server in Java and want to require users to provide login and password and then use their login-name internally to provide different permissions, different quotas, etc... for different users. How can I do that with Java? I prefer to use standard HTTP method for this (classic pop-up login/password dialog in client browser). This is typical solution for all password-protected proxies.
This question sounds so simple... How to popup a standard dialog asking for login/password in client browser and get its values for farther processing. But I googled for the solution and found nothing. In the Internet, there is a lot of information about how I can use password-protected proxy but none about how I can write one myself with Java.
Thanks. I need at least some clues...

Answer 1

I'm asking exactly what I'm asking for in the title :) . Maybe I need to give an example with additional explanation?
I'm writing a proxy. It has different settings for each user so it must recognize user name and password. Of course, user want to use a browser or other program (possibly another proxy - for example Proxomitron or Privoxy to filter banners and ads) to make requests via my proxy. Browser (not my proxy) should pop-up a dialog asking for a login and password if my proxy server will require authorization. Of course not every program will pop-up a dialog: for example in case of Privoxy or Proxomitron user must provide login and password for parent proxy. In this example "parent proxy" is my proxy. Question is: how I can request HTTP authorization (by sending Proxy-Authenticate) and handle the input? Is there any standard API for that in Java?
There is big difference between standard HTTP authorization and custom pop-up dialog or custom web-interface login page. In first case user can use standard settings in his/her program/browser to provide password automatically (in this case user just need to enter his/her password once). HTTP authorization is the standard. My proxy need to handle Proxy-Authorization request-header field.
The Proxy-Authorization request-header field allows the client to identify itself (or its user) to my proxy which (should be able to) require authentication. The Proxy-Authorization field value consists of credentials containing the authentication information of the user agent for the proxy and/or realm of the resource being requested.
So more complete question would be: is there standard API or third-party API in Java for requesting Proxy-Authorization field from a client and process its values (for example: if password and login is correct then user is allowed to use the proxy; if not user will be asked for login and password again).
If someone knows proxy server (with source code in Java) which can use standard password protection this will be good answer to my question too.
Unfortunately it seems that I will need to write account-management code for my proxy myself. Oh, this isn't too hard but for C/C++ there is a lot of examples and ready-to-use pieces of code which I can use immediately. This is why I'm asking here this question: before I will write HTTP authorization class in Java from scratch I want to make sure there is no "ready-to-use piece of code". I don't want to "reinvent the wheel".
For now, I even cannot find a proxy server with Java source code with ability to use standard password protection to prevent access for non-authorized users. So I'm asking here if there is ready-to-use API (class) for doing HTTP authorization or I need to write one myself.
Message was edited by:
Dark_Dragon