Album IDs can be passed via the query string parameter "aid", but there is no support for passing usernames and passwords this way - the main reason being it violates security best practices to pass a password in plain text in an URL.
How about this: just redirect them to their album. Disable anonymous access and GSP will automatically throw up the login prompt where they can enter their credentials. The biggest advantage to this approach is you use a shipping build of GSP, enabling you to easily upgrade when new versions come out.
If you really want to automate the process - which I understand - then you need to encrypt the username and password in the URL. Setting up a custom build that handles this wouldn't be too much work. If you want to hire me, contact me via roger*at*techinfosystems*dot*com with more details about your requirements and I'll give you a quote.
Roger Martin
Creator and Lead Developer of Gallery Server Pro