one easy way of doing that would be to set up security restrictions through the security subsystem. It can also be combined with something like IP range restcitions for particular users.
If this does not solve the problem, probably there would be ways to use the same backend with two FE wars, but i can’t think of a solution at the top of my head - perhaps other people have thouhts on that…
With some manual changes in build.gradle you can have multiple web modules in a project, but only one module will be supported in Studio. So you will not be able to work with screens of the additional module in Studio, which as I think is a major drawback.
An alternative and recommended approach is to have one module but to deploy it 2 times with different parameters - for example, change cuba.menuConfig app property to replace the main menu for the second web app.
If you still decide to go for multiple modules, let us know and I will share a sample project having 2 web modules.