Clients and back end user management in website

I’m going to build a sample website to manage documents of tax refund agency. Clients can register through the website and able to submit necessary documents. Once after the submission completed an agent from the company will review the documents.

I can develop the user registration and login for clients in normal way. But how do I create a registration and login procedure for employees of the company? Is it possible to use the same User table for agents also? What may be the professional way to do this?taxrefund