Programming: Need to integrate 2 or 3 wordpress plugins so that they use the same password

We have a wordpress website up and running and we will be installing a plugin called User Access Control which controls access to private pages and Mingle Forums. We need them both to use the same password so that the clients will not need to log in at 2 separate places on the same site. So when the clients log in at one page they will automatically be logged in to both the User Access Control and the Mingle Forum. We may also want to be able to pass the same username and password to a 3 party site when the user clicks to use it. Its a program called mycase and it is a cloud storage program that we will be linking to. So if you can also include a quote for passing it to another page that would be good.