DirectAccess and Azure Multifactor Authentication

Introduction

DirectAccess and Azure Multifactor AuthenticationDirectAccess can be configured to enforce strong user authentication using smart cards or one-time passwords (OTP). This provides the highest level of assurance for remote users connecting to the internal network via DirectAccess. OTP solutions are commonly used because they require less administration and are more cost effective than typical smart card implementations. Most OTP solutions will integrate with DirectAccess as long as they support Remote Access Dial-In User Service (RADIUS).

DirectAccess and Azure Multifactor Authentication

Azure Authentication-as-a-Service

Azure Multifactor Authentication (MFA) is a popular OTP provider used to enable strong user authentication for a variety of platforms, including web sites and client-based VPN. Unfortunately, it doesn’t work with DirectAccess. This is because Azure MFA uses a challenge/response method for which DirectAccess does not support. To use OTP with DirectAccess, the user must be able to enter their PIN and OTP immediately when prompted. There is no provision to begin the authentication process and wait for a response from the OTP provider.

PointSharp ID Multifactor Authentication

An excellent alternative to Azure MFA is PointSharp ID. PointSharp is a powerful OTP platform that integrates easily with DirectAccess. It is also very flexible, allowing for more complex authentication schemes for those workloads that support it, such as Exchange and Skype for Business.

DirectAccess and Azure Multifactor AuthenticationEvaluate PointSharp

You can download a fully-functional trial version of PointSharp ID here (registration required). The PointSharp ID and DirectAccess integration guide with detailed step-by-step instructions for configuring DirectAccess and PointSharp ID can be downloaded here. Consulting services are also available to assist with integrating PointSharp ID with DirectAccess, VPN, Exchange, Skype for Business, Remote Desktop Services, or any other solution that requires strong user authentication. More information about consulting services can be found here.

Additional Information

PointSharp Multifactor Authentication
Configure DirectAccess with OTP Authentication
DirectAccess Consulting Services
Implementing DirectAccess with Windows Server 2016

DirectAccess and OTP with PointSharp ID Webinar

Integrating multifactor authentication is essential for providing the highest level of security and assurance for DirectAccess clients. Smart cards work well for this, but they impose a heavy burden in terms of expense and administrative overhead. A more effective alternative is to use a One-Time Password (OTP) solution such as PointSharp ID.

DirectAccess and PointSharp ID Webinar

To learn more about the PointSharp ID OTP solution and how it integrates with DirectAccess, join me for a live webinar on Tuesday, July 27, 2106 at 10:00AM PDT where I’ll discuss the following topics.

  • What DirectAccess security risks can be mitigated with OTP?
  • What are the supporting infrastructure requirements for OTP authentication?
  • How to integrate the PointSharp IP solution with DirectAccess

You can register for this free live webinar here.

Configuring Multiple Windows Server 2012 R2 DirectAccess Instances

DirectAccess in Windows Server 2012 R2 supports many different deployment configurations. It can be deployed with a single server, multiple servers in a single location, multiple servers in multiple locations, edge facing, in a perimeter or DMZ network, etc.

Global Settings

There are a number of important DirectAccess settings that are global in scope and apply to all DirectAccess clients, such as certificate authentication, force tunneling, one-time password, and many more. For example, if you configure DirectAccess to use Kerberos Proxy instead of certificates for authentication, Windows 7 clients are not supported. In this scenario it is advantageous to have a second parallel DirectAccess deployment configured specifically for Windows 7 clients. This allows Windows 8 clients to take advantage of the performance gains afforded by Kerberos Proxy, while at the same time providing an avenue of support for Windows 7 clients.

Parallel Deployments

To the surprise of many, it is indeed possible to deploy DirectAccess more than once in an organization. I’ve been helping customers deploy DirectAccess for nearly five years now, and I’ve done this on more than a few occasions. In fact, there are some additional important uses cases that having more than one DirectAccess deployment can address.

Common Use Cases

QA and Testing – Having a separate DirectAccess deployment to perform testing and quality assurance can be quite helpful. Here you can validate configuration changes and verify updates without potential negative impact on the production deployment.

Delegated Administration – DirectAccess provides support for geographic redundancy, allowing administrators to create DirectAccess entry points in many different locations. DirectAccess in Windows Server 2012 R2 lacks support for delegated administration though, and in some cases it may make more sense to have multiple separate deployments as opposed to a single, multisite deployment. For example, many organizations are divided in to different business units internally and may operate autonomously. They may also have different configuration requirements, which can be better addressed using individual DirectAccess implementations.

Migration – If you have currently deployed DirectAccess using Windows Server 2008 R2 with or without Forefront UAG 2010, migrating to Windows Server 2012 R2 can be challenging because a direct, in-place upgrade is not supported. You can, however, deploy DirectAccess using Windows Server 2012 R2 in parallel to your existing deployment and simply migrate users to the new solution by moving the DirectAccess client computer accounts to a new security group assigned to the new deployment.

Major Configuration Changes – This strategy is also useful for scenarios where implementing changes to the DirectAccess configuration would be disruptive for remote users. For example, changing from a single site to a multisite configuration would typically require that all DirectAccess clients be on the LAN or connect remotely out-of-band to receive group policy settings changes after multisite is first configured. In addition, parallel deployments can significantly ease the pain of transitioning to a new root CA if required.

Unique Client Requirements – Having a separate deployment may be required to take advantage of the unique capabilities of each client operating system. For example, Windows 10 clients do not support Microsoft Network Access Protection (NAP) integration. NAP is a global setting in DirectAccess and applies to all clients. If you still require NAP integration and endpoint validation using NAP for Windows 7 and Windows 8.x, another DirectAccess deployment will be required to support Windows 10 clients.

Requirements

To support multiple Windows Server 2012 R2 DirectAccess deployments in the same organization, the following is required:

Unique IP Addresses – It probably goes without saying, but each DirectAccess deployment must have unique internal and external IPv4 addresses.

Distinct Public Hostname – The public hostname used for each deployment must also be unique. Multi-SAN certificates have limited support for DirectAccess IP-HTTPS (public hostname must be the first entry in the list), so consider using a wildcard certificate or obtain certificates individually for each deployment.

Group Policy Objects – You must use unique Active Directory Group Policy Objects (GPOs) to support multiple DirectAccess deployments in a single organization. You have the option to specify a unique GPO when you configure DirectAccess for the first time by clicking the Change link next to GPO Settings on the Remote Access Review screen.

Configuring Multiple Windows Server 2012 R2 DirectAccess Instances

Enter a distinct name for both the client and server GPOs. Click Ok and then click Apply to apply the DirectAccess settings for this deployment.

Configuring Multiple Windows Server 2012 R2 DirectAccess Instances

Windows 7 DirectAccess Connectivity Assistant (DCA) GPOs – If the DirectAccess Connectivity Assistant (DCA) v2.0 has been deployed for Windows 7 clients, separate GPOs containing the DCA client settings for each individual deployment will have to be configured. Each DirectAccess deployment will have unique Dynamic Tunnel Endpoint (DTE) IPv6 addresses which are used by the DCA to confirm corporate network connectivity. The rest of the DCA settings can be the same, if desired.

Supporting Infrastructure

The rest of the supporting infrastructure (AD DS, PKI, NLS, etc.) can be shared between the individual DirectAccess deployments without issue. Once you’ve deployed multiple DirectAccess deployments, make sure that DirectAccess clients DO NOT belong to more than one DirectAccess client security group to prevent connectivity issues.

Migration Process

Moving DirectAccess client computers from the old security group to the new one is all that’s required to migrate clients from one DirectAccess deployment to another. Client machines will need to be restarted to pick up the new security group membership, at which time they will also get the DirectAccess client settings for the new deployment. This works seamlessly when clients are on the internal network. It works well for clients that are outside the network too, for the most part. Because clients must be restarted to get the new settings, it can take some time before all clients finally moved over. To speed up this process it is recommended that DirectAccess client settings GPOs be targeted at a specific OUs created for the migration process. A staging OU is created for clients in the old deployment and a production OU is created for clients to be assigned to the new deployment. DirectAccess client settings GPOs are then targeted at those OUs accordingly. Migrating then only requires moving a DirectAccess client from the old OU to the new one. Since OU assignment does not require a reboot, clients can be migrated much more quickly using this method.

Summary

DirectAccess with Windows Server 2012 R2 supports many different deployment models. For a given DirectAccess deployment model, some settings are global in scope and may not provide the flexibility required by some organizations. To address these challenges, consider a parallel deployment of DirectAccess. This will enable you to take advantage of the unique capabilities of each client operating system, or allow you to meet the often disparate configuration requirements that a single deployment cannot support.

Configure DirectAccess with OTP Authentication

Updated 6/10/2015: This post was revised to include instructions for enabling OTP support for Windows 7 clients and for configuring OTP on the DirectAccess server using the Remote Access Management console.

Introduction

DirectAccess in Windows Server 2012 R2 provides significantly improved authentication over traditional client-based VPN solutions. When configured to use certificate authentication (a recommended best practice) the DirectAccess client is authenticated using its machine certificate and its Active Directory computer account. Once the client machine has been authenticated, the user is also authenticated via Kerberos against a live domain controller over the existing DirectAccess connection. These multiple authentication steps provide a high level of assurance for DirectAccess-connected clients. If that’s not enough to meet your needs, additional strong user authentication is supported using dynamic One-Time Passwords (OTP).

Drawbacks for DirectAccess with OTP

While OTP provides an additional level of assurance, it does come with a few drawbacks. OTP adds additional complexity and makes troubleshooting more difficult. OTP cannot be configured with force tunneling; the two security features are mutually exclusive. DirectAccess OTP does not support RADIUS challenge-response. For Windows 7 clients, the DirectAccess Connectivity Assistant (DCA) v2.0 must be deployed. In addition, enabling OTP with DirectAccess disables the use of null cipher suites for IP-HTTPS. This can potentially have a negative effect on performance and scalability (more details here). Also, OTP fundamentally breaks the seamless and transparent nature of DirectAccess.

Configuring DirectAccess OTP

OTP for DirectAccess makes use of short-lived certificates for user authentication. Thus, enabling OTP for DirectAccess requires making changes to the internal Public Key Infrastructure (PKI). DirectAccess in Windows Server 2012 R2 can be configured to use the same Certificate Authority (CA) that is used to issue computer certificates to the DirectAccess clients and servers. This differs from DirectAccess with Forefront Unified Access Gateway (UAG) 2010, where a separate, dedicated CA was required.

To configure DirectAccess OTP, follow the instructions below.

OTP Certificate Request Signing Template

Open the Certification Authority management console, right-click Certificate Templates, and then choose Manage. Alternatively you can enter certtmpl.msc in the Start/Run box or search from the Windows Start menu. Right-click the Computer template and choose Duplicate Template. On a Windows Server 2008 or 2008 R2 CA, select Windows Server 2008 Enterprise when prompted for the duplicate certificate template version.

Configure DirectAccess with OTP Authentication

On a Windows Server 2012 or 2012 R2 CA, select Compatibility tab and then select Windows Server 2008 R2 for the Certification Authority and Windows 7/Windows Server 2008 R2 for the Certificate recipient.

Configure DirectAccess with OTP Authentication

Select the General tab and provide a descriptive name for the Template Display Name. Specify a validity period of 2 days and a renewal period of 1 day.

Configure DirectAccess with OTP Authentication

Select the Security tab and click Add. Click Object Types and then select Computers and click Ok. Enter the names of each DirectAccess server separated by semicolons and click Check Names. Click Ok when finished. For each DirectAccess server, grant Read, Enroll, and Autoenroll permissions. Select Authenticated Users and remove any permissions other than Read. Select Domain Computers and remove the Enroll permission. Select Domain Admins and grant Full Control permission. Do the same for Enterprise Admins.

Configure DirectAccess with OTP Authentication

Select the Subject Name tab and choose the option to Build from this Active Directory information. Select DNS name in the Subject name format drop-down list and confirm that DNS name is checked under Include this information in alternate subject name.

Configure DirectAccess with OTP Authentication

Select the Extensions tab, highlight Application Policies and click Edit.

Configure DirectAccess with OTP Authentication

Remove all existing application policies and then click Add and then New. Provide a descriptive name for the new application policy and enter 1.3.6.1.4.1.311.81.1.1 for the Object Identifier. Click Ok for all remaining dialog boxes.

Configure DirectAccess with OTP Authentication

OTP Certificate Template

In the Certificate Templates Console, right-click the Smartcard Logon certificate template and choose Duplicate Template. On a Windows Server 2008 or 2008 R2 CA, select Windows Server 2008 Enterprise when prompted for the duplicate certificate template version.

Configure DirectAccess with OTP Authentication

On a Windows Server 2012 or 2012 R2 CA, select the Compatibility tab and then select Windows Server 2008 R2 for the Certification Authority and Windows 7/Windows Server 2008 R2 for the Certificate recipient.

Configure DirectAccess with OTP Authentication

Select the General tab and provide a descriptive name for the Template Display Name. Specify a validity period of 1 hour and a renewal period of 0 hours.

Configure DirectAccess with OTP Authentication

Note: It is not possible to set the validity period to hours on a Windows Server 2003 Certificate Authority (CA). As a workaround, use the Certificate Templates snap-in on another system running Windows 7/Windows Server 2008 R2 or later. Also, if the CA is running Windows Server 2008 R2, the template must be configured to use a Renewal Period of 1 or 2 hours and a Validity Period that is longer but no more than 4 hours.

Select the Security tab, then highlight Authenticated Users and grant Read and Enroll permissions. Select Domain Admins and grant Full Control permission. Do the same for Enterprise Admins.

Configure DirectAccess with OTP Authentication

Select the Subject Name tab and choose the option to Build from this Active Directory information. Select Fully distinguished name in the Subject name format drop-down list and confirm that User principal name (UPN) is checked under Include this information in alternate subject name.

Configure DirectAccess with OTP Authentication

Select the Server tab and choose the option Do not store certificates and requests in the CA database. Clear the checkbox next to Do not include revocation information issued in certificates.

Configure DirectAccess with OTP Authentication

Select the Issuance Requirements tab and set the value for This number of authorized signatures to 1. Confirm that Application Policy is selected from the Policy type required in signature drop-down list and choose the OTP certificate request signing template created previously.

Configure DirectAccess with OTP Authentication

Select the Extensions tab, highlight Application Policies and click Edit. Highlight Client Authentication and click Remove. Ensure that the only application policy listed is Smart Card Logon.

Configure DirectAccess with OTP Authentication

Certificate Authority Configuration

In the Certificate Authority management console, right-click Certificate Templates, choose New, and then Certificate Template to Issue. Highlight both of the certificate templates created previously and click Ok.

Configure DirectAccess with OTP Authentication

Open an elevated command prompt and enter the following command:

certutil.exe -setreg dbflags +DBFLAGS_ENABLEVOLATILEREQUESTS

Configure DirectAccess with OTP Authentication

Restart the Certificate Authority service by right-clicking the CA in the Certificate Authority management console and choosing All Tasks and then Stop Service. Once complete, repeat these steps and choose Start Service.

DirectAccess Server Configuration

In the Remote Access Management console, select DirectAccess and VPN under Configuration in the navigate pane and then click Edit on Step 2 – Remote Access Server. Select Authentication, choose Two-factor authentication (smart card or one-time password (OTP)), and then check the option to Use OTP.

Configure DirectAccess with OTP Authentication

Click Next and then add the RADIUS servers that will be used for OTP authentication. Provide the hostname, FQDN, or IP address of the server, the shared secret, and specify the service port.

Configure DirectAccess with OTP Authentication

Click Next, select the CA server that will be used to issue certificates to DirectAccess clients for OTP authentication, and then click Add.

Click Next, select the CA server that will be used to issue certificates to DirectAccess clients for OTP authentication, and then click Add.

Note: When performing this step you may receive the following error.

No CA servers can be detected, and OTP cannot be configured. Ensure that
servers added to the list are available on each domain controller in the
corporate network.

Configure DirectAccess with OTP Authentication

If this occurs, close out of the Remote Access Management console and install this hotfix.

Click Next and select the certificate templates to be used for the enrollment of certificates that are issued for OTP authentication. Also select a certificate template used to enroll the certificate used by the DirectAccess server to sign OTP certificate enrollment requests.

Configure DirectAccess with OTP Authentication

Click Next and specify whether selected DirectAccess users can authenticate with a user name and password when OTP authentication is disabled. If some users need to be exempted from using OTP, specify the security group as required and click Finish.

Configure DirectAccess with OTP Authentication

Click Edit on Step 3 – Infrastructure Servers. Select Management and add the CA server used for OTP authentication to the list of management servers.

Configure DirectAccess with OTP Authentication

Click Ok and then Finish. Click Finish once more and then apply the changes.

DirectAccess OTP Client Experience

When a DirectAccess client is outside of the corporate network and has established DirectAccess connectivity, users can log on to their machine and access their desktop, but they will not be able to access corporate resources without first providing their OTP.

For Windows 8 clients, swipe in from the right side of the screen or press Window Key + I and click on the active network connection. The DirectAccess Workplace Connection will indicate that action is needed. Clicking on the Workplace Connection will indicate that credentials are needed. Clicking Continue will prompt the user to press Ctrl+Alt+Delete and provide their OTP.

Configure DirectAccess with OTP Authentication

For Windows 7 clients, an alert from the DirectAccess Connectivity Assistant (DCA) in the system tray will indicate that Windows needs your smart card credentials. Clicking on the notification Window will prompt the user to provide their OTP.

Configure DirectAccess with OTP Authentication

Alternatively the user can click on the DCA icon in the system tray and then click Lock and unlock your computer with a smartcard or a one-time password. The user will then press CTRL+ALT+DELETE, choose Other Credentials, select One-time password (OTP), and then provide their OTP.

Configure DirectAccess with OTP Authentication

Summary

Using dynamic, one-time passwords is an effective way to provide the highest level of assurance for remote DirectAccess clients. It does come with some potential drawbacks, so be sure to consider those before implementing OTP.

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