Users in IWP

I'm considering implementation of an IWP solution. I've never used IWP before, having always either shared a filemaker file over a local network, or creating a web solution via lasso.

This db includes a list of local farmers who would be able to edit their own record. In a lasso solution, each of their records would have user and pass fields. It is not clear to me how this works in IWP. Would all users access the db initially with the same user/pass and then enter their personal user/pass that would be passed into a script that would find their personal record for editing? Seems like there's some new challenges to achieve easy navigation and security at the same time..can anyone offer the conceptual strategy for approaching this? Is it more like sharing a file on a network or more like using middleware like lasso?