Exchange ActiveSync in Exchange Server 2007 allows Windows Mobile-based devices and Exchange ActiveSync-enabled third-party devices to synchronize e-mail, calendar, contact, and task information that is stored on the user's Exchange server, and to retain access to this information when the mobile device is online or offline.
Exchange Server 2007 adds the ability to authenticate an ActiveSync connection using certificate-based authentication. Prior to ISA Server 2006, to publish ActiveSync with certificate-based authentication, you had to publish ActiveSync in tunnel mode. When you publish a site in tunnel mode, you lose the benefit of ISA Server being able to inspect the SSL traffic.
ISA Server 2006 supports Kerberos constrained delegation, which allows ISA Server to authenticate client connections with a client certificate and issues a Kerberos ticket to the published Web server. When Kerberos constrained delegation is configured properly, the published Web server accepts the Kerberos ticket instead of client credentials.
This appendix provides information about the configuration changes to the Exchange Client Access server, to the back-end servers, and to the ISA Server computer, which are required to successfully publish ActiveSync with client certificate-based authentication through ISA Server 2006.
The following are required to configure certificate-based authentication with ActiveSync through ISA Server 2006:
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Raise the domain functional level to Windows Server 2003.
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Configure Kerberos constrained delegation and protocol transitioning for:
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ISA Server
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Exchange Client access servers
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Configure Integrated Windows authentication for the Exchange Client Access servers.
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Create and assign an Exchange ActiveSync mailbox policy. For more information about creating and assigning an Exchange ActiveSync mailbox policy, see the Exchange 2007 product Help.
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Create a Web listener with client authentication set to client certificate authentication.
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Create an Exchange publishing rule, setting the authentication delegation to Kerberos constrained delegation.
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Test the new configuration.
Raising the Domain Functional Level to Windows Server 2003
For Kerberos constrained delegation to work properly, you need to confirm that the Active Directory domain is working at a Windows Server 2003 native mode level.
To raise the domain functional level to Windows Server 2003
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Click Start, point to Program Files, point to Administrative Tools, and then click Active Directory Users and Computers.
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The change in steps 2, 3, and 4 are permanent. You cannot undo these actions.
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Right-click the domain, and then select Raise Domain Functional Level.
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In the Raise Domain Functional Level box, select Windows Server 2003 from the list, and then click Raise.
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Click OK.
Configuring Constrained Delegation and Protocol Transitioning
Kerberos is a network authentication protocol that authenticates the identity of users who are trying to log on to a network, and encrypts their communications through secret key cryptography.
You must configure Kerberos constrained delegation when ISA Server is configured to authenticate the user through a client certificate and then impersonate that user to the Exchange front-end server. The Exchange Client Access server will then impersonate the user when you access the user's e-mail, calendar, contact, and task information in the Exchange back-end server where the user's mailbox is located. This is required because ISA Server cannot delegate the client certificate presented to it by the client.
When you want to configure Kerberos constrained delegation, so that the Exchange Client Access server trusts the Kerberos ticket from the ISA Server computer, the configuration is done on the ISA Server computer account. To configure Kerberos constrained delegation, so that the Exchange Mailbox servers trust the Kerberos ticket issued from the Exchange Client Access servers, the configuration is done on the Exchange Client Access servers computer account.
For more information, see Kerberos Authentication in Windows Server 2003.
Active Directory Users and Computers is an MMC snap-in that is a standard part of Microsoft Windows Server operating systems. However, when you install Exchange Server 2003, the Setup wizard automatically extends the functionality of Active Directory Users and Computers to include Exchange-specific tasks.
You start Active Directory Users and Computers from either an Exchange server or from a workstation that has the Exchange management tools installed.
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If the Active Directory Users and Computers snap-in is installed on a computer that does not have Exchange Server or the Exchange Server management tools installed, you cannot perform Exchange Server tasks from that computer.
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The Delegation tab that is referenced in the following procedures lets you configure delegation in three ways:
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Not allowed Select the Do not trust this computer for delegation option.
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Allowed for all services Select the Trust this computer for deletion to any service (Kerberos only) option. Refers to the Windows 2000 Server delegation method.
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Allowed for only a limited set of services Select the Trust this computer for delegation to specified services only option. Refers to the constrained delegation method available with Windows Server 2003.
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The ISA Server and Exchange Client Access servers need to be in the same domain.
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To configure Kerberos constrained delegation on the ISA Server computers, perform the following procedure.
To use Active Directory Users and Computers to configure constrained delegation and protocol transitioning
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Click Start, point to Program Files, point to Administrative Tools, and then click Active Directory Users and Computers.
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In the console tree, click your Domain and expand the tree view.
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Click Computers and expand the tree view. From the list of computers, right-click the ISA Server computer, click Properties, and then click the Delegation tab.
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On the Delegation tab, select Trust the computer for designation of specified services only, and then click Add.
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Select Use any authentication protocol to enable protocol transitioning, and then click Add.
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Click Users or Computers, type the name of the Exchange Client Access server, and then click OK.
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Select HTTP and W3SVC, and then click OK two times.
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Note Perform this procedure for each ISA Server computer that will be publishing Exchange ActiveSync.
To configure Kerberos constrained delegation for the Exchange Client Access servers, perform the following procedure.
To use Active Directory Users and Computers to configure constrained delegation and protocol transitioning, follow these steps from the Client Access server
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Click Start, point to Program Files, point to Administrative Tools, and then click Active Directory Users and Computers.
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In the console tree, click your Domain and expand the tree view.
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Click Computers and expand the tree view. From the list of computers, right-click the Exchange Client access server, click Properties, and then click the Delegation tab.
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On the Delegation tab, select Trust the computer for designation of specified services only, and then click Add.
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Select Use any authentication protocol to enable protocol transitioning, and then click Add.
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Click Users or Computers, type the name of the Exchange Mailbox server or servers, and then click OK.
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Select HTTP and W3SRV, and then click OK two times.
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Right-click the back-end Exchange computer, click Properties, and then click Delegation.
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On the Delegation tab, select Trust the computer for designation of specified services only. If the Mail box server is a domain controller, it is already configured to trust the computer for designation of specified services only.
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this procedure for each Exchange Client Access server in your environment that is providing Exchange ActiveSync services.
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Configuring Integrated Windows Authentication on the Exchange Front-End Servers
For the Exchange front-end servers to accept the Kerberos ticket, the ActiveSync directory needs to be configured to accept Integrated Windows authentication in IIS Manager.
Perform the following procedure to configure Integrated Windows authentication on the Exchange front-end servers.
To configure Integrated Windows authentication for the ActiveSync directory in IIS Manager
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In IIS Manager, double-click the local computer, right-click the ActiveSync directory you want to configure, and then click Properties.
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Click the Directory Security tab.
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In the Authentication and access control section, click Edit.
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In the Authenticated access section, select Integrated Windows Authentication.
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Click OK twice.
Creating a New Web Listener
You need to create a new Web listener with client authentication configured with client certificate authentication.
Follow the instructions in the topic Create a Web listener, with the following change:
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On the Authentication Settings page, select SSL Client Certificate Authentication.
Creating a New Exchange Publishing Rule
To create a new Exchange publishing rule, follow the instructions in the topic Create an Exchange Web client access publishing rule, with the following changes:
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On the Select Services page, select Exchange ActiveSync.
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On the Authentication Delegation page, select Kerberos constrained delegation. The service principle name will be automatically entered, based on the information you entered in the Internal site name box on the Internal Publishing Details page.