Selecting Login Portal Plugin

I work for a small but growing nonprofit and as part of further developing our website, we’re looking to set up a login portal for our Board of Directors. I’m having a hard time identifying/choosing a plugin to do that.

What we are looking for is a fairly simple portal login where each of our board members can be given an individual login and password to access a shared page where things like important documents, meeting minutes, etc. can be accessed. The goal is to allow new board members to be easily given a login when they join the board, but for an individual login to also be easily struck when someone cycles off of the board, since this would be easier and more secure than a basic password-locked page.