Accessing an Independent Application from Withing a CodeIgniter Application.

I built a small database resource for a client using vanilla PHP several years ago. I have just completed a custom CRM for the client using CodeIgniter 3. The client wants to be able to access the database resource from within his CRM, instead of linking to it from his website.

I have three issues to solve:

1. Right now I have the resource in a directory independent of the CRM, and just link to it. Is it possible to place the resource directory inside the root folder of the CRM? Would there be an advantage there?

2. How can I piggy-back on the sessions of the CRM so that I can make sure a user is logged in to the CRM before he can access the resource, instead of directly?

3. How can I redirect the user back to the CI page he came from after he is finished with the resource? I have 5 roles in the CRM, one of which will go directly to the resource when they log in, the other four will go to the resource from a menu item on their particular home page in the CRM.

Best scenario would be to redo the resource as a CI application, and part of the CRM but I don't have time right now to do that. I have two weeks to get this done.

Thanks.