Linux Winodws C++ GURU

I would like to create a proprietary logon for Linux systems. It will use a "device" to verify the user. I will provide sample source for the device (SDK) etc. The user will present the device and the application will check the credentials to with a database to verify the user, and then allow him to log on or not. When replying please describe a) have you done this before or similar experience b) how you would do this c) what language would you use I am flexible, if you want to try and start we can do it in two stages. A "try" stage for x$ to see what results are achieved. If positive we can keep going. If it looks to difficult we can stop at that stage. The x$ will be paid to you in any event.