Which change must be implemented to allow the contractors and employees to access the portal?

A customer wants to provide wireless access to contractors using a guest portal on Cisco ISE. The portal Is also used by employees A solution is implemented, but contractors receive a certificate error when they attempt to access the portal Employees can access the portal without any errors .

Which change must be implemented to allow the contractors and employees to access the portal?
A . Install a trusted third-party certificate on the Cisco IS
C . Install an Internal CA signed certificate on the contractor devices
D . Install an internal CA signed certificate on the Cisco ISE
E . install a trusted third-party certificate on the contractor devices.

Answer: A