I'm referring limit number device/devices associating to SSID itself. Eg: Company A have 50 staff. Limit it only to 50 of company A laptops. No mobile device is allowed to access. Something like access control.
I believe the L2 ACL should do the job. You can create a L2 ACL with the list of client MAC which you want to allow and call it on the WLAN. You can broadcast these SSIDs on the APs you want, which will allow only the clients listed.