Get MAC of user

Hi all,
I have idea to help our customer easy connect our wifi via hotspot user when they come to our company.
My idea is:
1 - Configure hotspot on wifi system and set default user login.
2 - When our customer come to our company, they can access wifi with default user.
3 - I created script for default user, after new device access wifi by default user then system send email to me with content: IP, MAC.
4 - After customer connected, a webpage will popup and require input some information: Name, Company name, MAC. and submit this form. After customer submit form, system send email to me.
5 - I will compare MAC address of step 3 and 4. if the same, i will trust this MAC address.

But our customer cannot how to view MAC address to input into request form on step 4. Could you help me automatically get MAC without customer input on step 4?
Or you have some idea for this please recommend me.

Thank you.