Two companies need to implement an extranet overlay network solution by using a VPN tunnel...

Two companies need to implement an extranet overlay network solution by using a VPN tunnel over the internet to use each other ' s HTTP REST APIs. The solution must only provide data integrity because data confidentiality will be covered at the application layer The existing firewall devices will be used as VPN endpoints for the tunnel but they have limited available resources Which type of VPN tunnel must be deployed for the extranet service?