Step 3: Configure the Remote Access Server for OTP

Applies To: Windows Server 2012 R2, Windows Server 2012

Once the RADIUS server has been configured with software distribution tokens, communication ports are open, a shared secret has been created, user accounts corresponding to Active Directory have been created on the RADIUS server, and the Remote Access server has been configured as a RADIUS authentication agent, then the Remote Access server needs to be configured to support OTP.

3.1 Exempt users from OTP authentication (optional)

If specific users are to be exempted from OTP authentication, then these steps must be taken prior to the Remote Access configuration:

Create user exemption security group

1. Create a security group in Active Directory for the purpose OTP exemption.

2. Add all users to be exempted from OTP authentication to the security group.

   Note

   Make sure to include only user accounts, and not computer accounts, in the OTP exemption security group.

3.2 Configure the Remote Access server to support OTP

To configure Remote Access to use two-factor authentication and OTP with the RADIUS server and certificate deployment from the previous sections, use the following steps:

Configure Remote Access for OTP

1. Open Remote Access Management and click Configuration.

2. In the DirectAccess Setup window, under Step 2 – Remote Access Server, click Edit.

3. Click Next three times, and in the Authentication section select both Two factor authentication and Use OTP, and ensure that Use computer certificates is checked.

   Note

   After OTP has been enabled on the Remote Access server, if you disable OTP by deselecting Use OTP, the ISAPI and CGI extensions will be uninstalled on the server.

4. If Windows 7 support is required, select the Enable Windows 7 client computers to connect via DirectAccess check box. Note: As discussed in the planning section, Windows 7 clients must have DCA 2.0 installed to support DirectAccess with OTP.

5. Click Next.

6. In the OTP RADIUS Server section, double-click the blank Server Name field.

7. In the Add a RADIUS Server dialog, type the name of the RADIUS server in the Server name field. Click Change next to the Shared secret field, and type the same password that you used when configuring the RADIUS server in the New secret and Confirm new secret fields. Click OK twice, and click Next.

   Note

   If the RADIUS server is in a domain that is different than the Remote Access server, then the Server Name field must specify the FQDN of the RADIUS server.

8. In the OTP CA Servers section select the CA servers to be used for the enrollment of OTP client authentication certificates, and click Add. Click Next.

9. In the OTP Certificate Templates section click Browse to select the certificate template used for the enrollment of certificates that are issued for OTP authentication.

   Note

   The certificate template for OTP certificates issued by the corporate CA must be configured without the "Do not include revocation information in issued certificates" option. If this option is selected during the certificate template creation, then OTP client computers will fail to logon properly.

   Click Browse to select a certificate template used to enroll the certificate used by the Remote Access server to sign OTP certificate enrollment requests. Click OK. Click Next.

10. If exempting specific users from DirectAccess with OTP is required, then in the OTP Exemptions section select Do not require users in the specified security group to authenticate using two-factor authentication. Click Security Group and select the security group that was created for OTP exemptions.

11. On the Remote Access Server Setup page click Finish.

12. In the DirectAccess Setup window, under Step 3 – Infrastructure Servers, click Edit.

13. Click Next two times, and in the Management section double-click the Management Servers field.

14. Enter the Computer name or Address of the CA server that is configured to issue OTP certificates, and click OK.

15. In the Remote Access Setup windows click Finish.

16. Click Finish on the DirectAccess Expert Wizard.

17. On the Remote Access Review dialog box click Apply, wait for the DirectAccess policy to be updated, and click Close.

18. On the Start screen, type powershell.exe, right-click powershell, click Advanced, and click Run as administrator. If the User Account Control dialog box appears, confirm that the action it displays is what you want, and then click Yes.

19. In the Windows PowerShell window, type gpupdate /force and press ENTER.

To configure Remote Access for OTP using PowerShell commands:

Windows PowerShell equivalent commands

The following Windows PowerShell cmdlet or cmdlets perform the same function as the preceding procedure. Enter each cmdlet on a single line, even though they may appear word-wrapped across several lines here because of formatting constraints.

To configure Remote Access to use two-factor authentication on a deployment that currently uses computer certificate authentication:

Set-DAServer -UserAuthentication TwoFactor

To configure Remote Access to use OTP authentication using the following settings:

• An OTP server named OTP.corp.contoso.com.

• A CA server named APP1.corp.contoso.com\corp-APP1-CA1.

• A certificate template named DAOTPLogon used for the enrollment of certificates that are issued for OTP authentication.

• A certificate template named DAOTPRA used to enroll the Registration Authority certificate used by the Remote Access server to sign OTP certificate enrollment requests.

Enable-DAOtpAuthentication -CertificateTemplateName 'DAOTPLogon' -SigningCertificateTemplateName 'DAOTPRA' -CAServer @('APP1.corp.contoso.com\corp-APP1-CA1') -RadiusServer OTP.corp.contoso.com -SharedSecret Abcd123$

After executing the PowerShell commands complete steps 12-19 from the previous procedure to configure the Remote Access server to support OTP.

3.3 Smart cards for additional authorization

On the Authentication page of Step 2 in the Remote Access Setup Wizard, you can require the use of smart cards for access to the internal network. When this option is selected, the Remote Access Setup Wizard configures the IPsec connection security rule for the intranet tunnel on the DirectAccess server to require tunnel mode authorization with smart cards. Tunnel mode authorization allows you to specify that only authorized computers or users can establish an inbound tunnel.

To use smart cards with IPsec tunnel mode authorization for the intranet tunnel, you must deploy a public key infrastructure (PKI) with smart cards infrastructure.

Because your DirectAccess clients are using smart cards for access to the intranet, you can also use authentication mechanism assurance, a feature of Windows Server 2008 R2, to control access to resources, such as files, folders, and printers, based on whether the user logged on with a smart card-based certificate. Authentication mechanism assurance requires a domain functional level of Windows Server 2008 R2.

Allowing access for users with unusable smart cards

To allow temporary access for users with smart cards that are unusable, do the following:

1. Create an Active Directory security group to contain the user accounts of users who temporarily cannot use their smart cards.

2. For the DirectAccess server Group Policy Object, configure global IPsec settings for IPsec tunnel authorization and add the Active Directory security group to the list of authorized users.

To grant access to a user that cannot use their smart card, temporarily add their user account to the Active Directory security group. Remove the user account from the group when the smart card is usable.

Under the covers: Smart card authorization

Smart card authorization works by enabling tunnel mode authorization on the intranet tunnel connection security rule of the DirectAccess server for a specific Kerberos-based security identifier (SID). For smart card authorization, this is the well-known SID (S-1-5-65-1), which maps to smart card-based logons. This SID is present in a DirectAccess client’s Kerberos token and is referred to as “This Organization Certificate” when configured in the global IPsec tunnel mode authorization settings.

When you enable smart card authorization in Step 2 of the DirectAccess Setup Wizard, the DirectAccess Setup Wizard configures the global IPsec tunnel mode authorization setting with this SID for the DirectAccess server Group Policy Object. To view this configuration in the Windows Firewall with Advanced Security snap-in for the DirectAccess server Group Policy Object, do the following:

1. Right click Windows Firewall with Advanced Security, and then click Properties.

2. On the IPsec Settings tab, in IPsec tunnel authorization, click Customize.

3. Click the Users tab. You should see the “NT AUTHORITY\This Organization Certificate” as an authorized user.