DirectAccess requires computer certificates to be installed on the DirectAccess server and DirectAccess clients. These certificates are used for IPsec, which provides a secure, encrypted communication channel between the DirectAccess client and the DirectAccess server. IPsec ensures the necessary integrity, confidentiality, and non-repudiation required for secure remote access. When using a Public Key Infrastructure (PKI) to issue computer certificates to DirectAccess clients, it can be helpful to automate this process by configuring certificate auto-enrollment using Active Directory group policy.
To begin, open the Group Policy Management Console and expand Domains. Next, expand your domain, right-click Group Policy Objects and choose New. Enter a descriptive name for the new GPO and click Ok. Right-click the GPO you just created and choose Edit. Expand Computer Configuration, Windows Settings, Security Settings, and Public Key Policies. Highlight Public Key Policies, and then double-click Certificate Services Client – Auto-Enrollment. For the Configuration Model choose Enabled. It is recommended that you also choose to Renew expired certificates, update pending certificates, and remove revoked certificates and Update certificates that use certificate templates.
Close out of the Group Policy Editor and then link this computer certificate auto-enrollment GPO to your domain. Target only DirectAccess client and server security groups with this GPO instead of all domain computers by configuring Security Filtering to apply this GPO only to DirectAccess client and server machines.
Finally, on your certificate server, right-click the DirectAccess certificate template, choose Properties, and then choose Security. Make certain the Enroll and Autoenroll permissions are set to Allow for all DirectAccess client and server security groups.