Login to your FW, Under User & Device click on LDAP Servers
Follow the image below and fill in with your domain and user details.
Test Connectivity, if you fill in the fields correctly you will get Success Popup.
Now please create Active Direcoty Group in your AD Server in this example we will call it VPN.
We create this group that only users that will be in this group will be allowed to connect to the VPN.
After we created VPN group and added users to it, we will go back to the FW and create SSLVPN group and assign to it the new VPN AD group that we just created.
Go to User Groups –> Add new group –>Give it a name –> Click on Add
Select your LDAP server and press OK.
After we created this group. lets add some users.
Last Step… you can now connect with your AD username and password using your vpn Client.