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Manual Chapter : NTLM Authentication for Microsoft Exchange Clients

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BIG-IP APM

  • 11.5.1
Manual Chapter
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Overview: Configuring APM for Exchange clients that use NTLM authentication

Access Policy Manager (APM) supports Microsoft Exchange clients that are configured to use NTLM, by checking NTLM outside of the APM session as needed. APM requires a machine account and an NTLM Auth configuration to perform these checks. APM requires an Exchange profile to support Microsoft Exchange clients, regardless of the authentication they are configured to use.

About using NTLM authentication

Microsoft software systems use NTLM as an integrated single sign-on (SSO) mechanism. However, in an Active Directory-based SSO scheme, Kerberos replaces NTLM as the default authentication protocol. NTLM is still used when a domain controller is not available or is unreachable, such as when the client is not Kerberos-capable, the server is not joined to a domain, or the user authenticates remotely over the web.

About configuration requirements for NTLM authentication

In Access Policy Manager, you need to configure these elements:

  • Machine account
  • NTLM authentication configuration
  • Kerberos SSO configuration
  • Exchange profile that specifies the NTLM authentication configuration and specifies Kerberos SSO configurations for the specific Microsoft Exchange services supported
  • Access profile that specifies the Exchange profile
  • Access policy
  • Pool of servers for the Exchange service to support Outlook Anywhere, supply a pool of Outlook Anywhere servers
  • Virtual server that specifies the access profile and the pool

You also need to configure a special account in Active Directory for Kerberos constrained delegation (KDC).

About reusing a machine account for different BIG-IP systems

You can use the same machine account for two BIG-IP systems when they are in an active-standby configuration. Otherwise, F5 recommends that you create a new NTLM machine account using the Access Policy Manager user interface on each BIG-IP system.

Creating a new NTLM machine account on each BIG-IP system is helpful, for example, when two systems independently update their configurations without propagating them, or when you replicate the configuration into different BIG-IP systems using any configuration replication method. If you export a configuration and import it on another system, the machine account is included; however, after the import completes, you still need a new machine account and an NTLM authentication configuration that uses the new machine account on the target system.

About Outlook Anywhere and NTLM authentication

Access Policy Manager supports Outlook Anywhere clients that are configured to use NTLM and HTTP Basic protocols independently. Typically, mobile devices use HTTP Basic authentication, while Outlook Anywhere clients can use both NTLM and HTTP Basic authentication. APM determines whether a client uses NTLM or HTTP Basic authentication and enforces the use of one or the other. After a client authenticates with NTLM or HTTP Basic, APM supports single sign-on with the back-end application or server using Kerberos constrained delegation (KCD).

Task summary for Exchange clients that use NTLM authentication

Task list

Configuring a machine account

You need to configure a machine account so that Access Policy Manager (APM) can establish a secure channel to a domain controller.
  1. On the Main tab, click Access Policy > Access Profiles > NTLM > Machine Account. A new Machine Account screen opens.
  2. In the Configuration area, in the Machine Account Name field, type a name.
  3. In the Domain FQDN field, type the fully qualified domain name (FQDN) for the domain that you want the machine account to join.
  4. Optional: In the Domain Controller FQDN field, type the FQDN for a domain controller.
  5. In the Admin User field, type the name of a user who has administrator privilege.
  6. In the Admin Password field, type the password for the admin user. APM uses these credentials to create the machine account on the domain controller. However, APM does not store the credentials and you do not need them to update an existing machine account configuration later.
  7. Click Join.
This creates a machine account and joins it to the specified domain.

Creating an NTLM Auth configuration

Create an NTLM Auth configuration to specify the domain controllers that a machine account can use to log in.
  1. On the Main tab, click Access Policy > Access Profiles > NTLM > NTLM Auth Configuration. A new NTLM Auth Configuration screen opens.
  2. In the Name field, type a name.
  3. From the Machine Account Name list, select the machine account configuration to which this NTLM Auth configuration applies. You can assign the same machine account to multiple NTLM authentication configurations.
  4. For each domain controller, type a fully qualified domain name (FQDN) and click Add.
    Note: You should add only domain controllers that belong to one domain.
    By specifying more than one domain controller, you enable high availability. If the first domain controller on the list is not available, Access Policy Manager tries the next domain controller on the list, successively.
  5. Click Finished.
This specifies the domain controllers that a machine account can use to log in.

Setting up a delegation account to support Kerberos SSO

Before you can configure Kerberos SSO in Access Policy Manager, you must create a delegation account in Active Directory. Note that for every server realm, you must create a delegation account in that realm.
  1. Open the Active Directory Users and Computers administrative tool and create a new user account. The user account should be dedicated for delegation and the Password never expires setting enabled.
  2. Run the setspn command-line tool for the user account from an elevated command prompt: The setspn command-line tool is available in Windows 2000 and Windows Server 2003 from Support Tools; it needs to be installed. The setspn tool is built into Windows Server 2008; it is available if you have the Active Directory Domain Services (AD DS) server role installed.
    1. Click the Windows Start button, right-click Command Prompt, and then click Run as administrator. An elevated command prompt opens.
    2. Type an setspn command. Example of command usage on Windows Server 2003: setspn -A HTTP/bigcompany.lab.appnet.com domainname\userfordelegation
      Note: In Windows Server 2008, use the newly introduced -L option instead of -A. It validates the unicity of the service principal name (SPN) in the domain.
  3. Return to the Active Directory Users and Computers screen to open your account again. A Delegation tab should appear.
  4. Click the Delegation tab.
  5. Select Trust this user for delegation to specified services only.
  6. Select Use any authentication protocol, and add all your services to the list under Services to which this account can present delegated credentials. Every service should have Service Type HTTP (or http) and host name of the pool member or web application resource host that you will use in your configuration.
  7. Click OK. This creates the new delegation account.

Creating a Kerberos SSO configuration in APM

Before you create a Kerberos SSO configuration in Access Policy Manager, create a delegation account in Active Directory.
To support Kerberos single sign-on authentication from APM, you must create a Kerberos SSO configuration.
  1. On the Main tab, click Access Policy > SSO Configurations > Kerberos. The SSO Configurations screen opens for Kerberos type.
  2. Click Create. The New SSO Configuration screen opens.
  3. In the Name field, type a name for the SSO configuration.
  4. In the Credentials Source area, specify the credentials that you want cached for Single Sign-On.
  5. In the Kerberos Realm field, type the name of the realm in uppercase. For example, MY.HOST.LAB.MYNET.COM
  6. In the Account Name field, type the name of the Active Directory account configured for delegation.
  7. In the Account Password and Confirm Account Password fields, type the delegation account password.
  8. Click Finished.

Configuring an Exchange profile

If any of the Microsoft Exchange clients you support authenticate using NTLM, you must first create these objects:

  • A machine account

  • An NTLM Auth configuration

  • At least one Kerberos SSO configuration

Note: For Access Policy Manager (APM) to support Kerberos SSO, a delegation account is required on Active Directory.
You create an Exchange profile to specify how to handle traffic from Microsoft Exchange clients.
  1. On the Main tab, click Access Policy > Application Access/Microsoft Exchange. A list of Exchange profiles displays.
  2. Click Create. A Create New Exchange Profile popup screen displays general settings.
  3. In the Exchange Name field, type a name for the Exchange profile.
  4. From the Parent Profile list, select a profile. The Exchange profile inherits settings from the parent profile that you select.
    Note: APM supplies a default Exchange profile named exchange.
  5. Repeat these steps for one or more Microsoft Exchange services:
    1. From Service Settings on the left, select an Exchange service. Settings for the service are displayed in the right pane.
    2. In the URL field, retain any default settings that are displayed or type a path to use to match the Exchange client. Default settings for this field are supplied in the default exchange profile.
    3. From the Front End Authentication list, select the type of authentication to use: Basic, Basic-NTLM, or NTLM. Only the applicable authentication types for the particular the Exchange service are included on the list.
      Note: If you select NTLM or Basic-NTLM, you must also select a configuration from NTLM Configuration list on the General Settings screen.
    4. From the SSO Configuration list, select an SSO configuration, if needed, for use after initial login. For Basic-NTLMand NTLM authentication types, only Kerberos SSO is supported.
    You configured settings for one or more Microsoft Exchange services.
  6. Click OK. The screen closes.
The Exchange profile is displayed on the list.
Apply this Exchange profile by adding it to an access profile.

Creating an access profile for Exchange clients

You create an access profile to provide the access policy configuration for a virtual server that establishes a secured session. You add an Exchange profile to the access policy to specify how to handle traffic from Microsoft Exchange clients.
  1. On the Main tab, click Access Policy > Access Profiles. The Access Profiles List screen opens.
  2. Click Create. The New Profile screen opens.
  3. In the Name field, type a name for the access profile.
  4. Optional: In the Configurations area from the Exchange list, select an Exchange profile. Exchange profiles specify any SSO configurations for Microsoft Exchange services, such as Autodiscover, Outlook Anywhere, and so on. The configuration in the Exchange profile is used for Microsoft Exchange clients regardless of any SSO configuration you select from the SSO Configuration list in this access profile.
  5. In the Language Settings area, add and remove accepted languages, and set the default language. A browser uses the highest priority accepted language. If no browser language matches the accepted languages list, the browser uses the default language.
  6. Click Finished.
The access profile appears in the Access Profiles List.

Configuring an access policy for NTLM authentication

You configure an access policy for NTLM authentication to support Outlook Anywhere clients that log in using NTLM to also gain SSO access to a backend server that is protected by Kerberos KCD.
Note: NTLM authentication occurs before an access policy runs. If NTLM authentication fails, an error displays and the access policy does not run.
  1. On the Main tab, click Access Policy > Access Profiles. The Access Profiles List screen opens.
  2. In the Access Policy column, click the Edit link for the access profile you want to configure. The visual policy editor opens the access policy in a separate screen.
  3. Click the (+) icon anywhere in the access policy to add a new action item. A popup screen opens, listing predefined actions on tabs such as General Purpose, Authentication, and so on.
  4. On the Endpoint Security (Server-Side) tab, select Client for MS Exchange and click Add Item to add the action to the access policy. A Client for MS Exchange action determines whether the client is using Microsoft Exchange or ActiveSync protocols. You must add this action before an NTLM Auth Result action. The Client for MS Exchange action popup screen opens.
  5. Click Save. The properties screen closes and the visual policy editor displays.
  6. Check whether the Outlook Anywhere client authenticated using NTLM.
    1. Click the [+] sign on the successful branch after the Client for MS Exchange action. An Add Item window opens.
    2. On the Authentication tab, select NTLM Auth Result.
    3. Click Add Item. A popup screen opens.
    4. Click Save. The properties screen closes and the visual policy editor is displayed.
  7. Configure a branch in the access policy for an Outlook Anywhere client that has authenticated using NTLM.
    1. Click the [+] sign on the successful branch after the NTLM Auth Result action. An Add Item window opens.
    2. On the Assignment tab, select SSO Credential Mapping and click Add Item. The SSO Credential Mapping screen opens.
    3. Click Save. The properties screen closes and the visual policy editor is displayed.
    4. On the fallback branch after the SSO Credential Mapping action, click the Deny ending. A popup screen opens.
    5. Select Allow and click Save. You have completed a branch in the access policy for an Outlook Anywhere client that, having previously authenticated with NTLM, has SSO (Kerberos KCD) access on the back end.
  8. Configure a branch in the access policy for an Outlook Anywhere client that uses HTTP Basic authentication.
    1. Click the [+] sign on the fallback branch after the NTLM Auth Result action. An Add Item window opens.
    2. On the Logon tab, select Logon Page and click the Add Item button. The Logon Page Agent properties screen opens.
    3. Make any changes that you require to logon page properties and click Save. The properties screen closes and the visual policy editor is displayed.
    4. On the Successful branch after the Logon Page action, add an authentication action.
    5. On the Successful branch after the authentication action, add an SSO Credential Mapping action.
    6. On the fallback branch after SSO Credential Mapping, change the ending from Deny to Allow.
    You have completed a branch in the access policy to authenticate an Outlook Anywhere client that uses HTTP Basic authentication and provides SSO (Kerberos KCD) access for the client on the back end.
  9. Optional: On the fallback branch after the MS Exchange Client action, configure a branch for a client that is not an Outlook Anywhere client. You could add Logon Page, authentication, and SSO Credential Mapping actions or other actions here.
  10. Click the Apply Access Policy link to apply and activate the changes to the access policy.
You have created an access policy that checks whether the client is an Outlook Anywhere client and whether such a client has authenticated using NTLM. If so, the policy provides SSO (Kerberos KCD) access on the backend server.
When NTLM authentication has passed, perform SSO Credential Mapping; otherwise, present a Logon Page and perform authentication. Example access policy with actions based on whether NTLM authentication occurred

Adding the access profile to the virtual server

You associate the access profile with the virtual server so that Access Policy Manager can apply the profile to incoming traffic.

  1. On the Main tab, click Local Traffic > Virtual Servers. The Virtual Server List screen opens.
  2. Click the name of the virtual server you want to modify.
  3. In the Access Policy area, from the Access Profile list, select the access profile.
  4. Click Update to save the changes.
Your access policy is now associated with the virtual server.

Maintaining a machine account

In some networks, administrators run scripts to find and delete outdated machine accounts on the domain controllers. To keep the machine account up-to-date, you can renew the password periodically.
  1. On the Main tab, click Access Policy > Access Profiles > NTLM > Machine Account. The Machine Account screen opens.
  2. Click the name of a machine account. The properties screen opens and displays the date and time of the last update to the machine account password.
  3. Click the Renew Machine Password button. The screen refreshes and displays the updated date and time.
This changes the machine account last modified time.
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