ASP.Net Is my web service secure enough?

I have a web service with several web methods, each web method requires the client computer to send its MAC address, and the server will check this client base for this information (if it is not valid and then returns an error) before than to proceed with further operations. The connection between the client and server is HTTPS. I have only about 20 clients. The question is, is my way of doing this right / safe or not? If not, is there an easy way to do this?

Thank,