ActiveSync Primer continued – The PROVISION command

February 3rd, 2011 § 1 comment

The PROVISION command and response is used by Exchange servers to communicate security policy settings to client devices.  If a security policy has been setup for an Exchange server, Exchange will not process any requests received from a client, until the policy settings are requested and acknowledged by the client. Please see the ActiveSync Provisioning Protocol Specification for more information about this command.

Depending upon the version of the Exchange server one of the following error messages are returned when a client issues a request before accepting the security policies.

  • HTTP/1.1 449 : Retry after sending a PROVISION command
  • HTTP/1.1 200 with a global status code in the body of the response of 142 (see example here).

A lot of this is repeated from the ActiveSync provisioning protocol documentation. However there are a few gotchas here, so I think it might be better to step through it.

Step 1: Client requests security policy from the server

Header

// Send a POST request to the mail server. Append
// the string “Microsoft-Server-ActiveSync” to the URL, and add the
// the following query strings as parameters to the URL as shown below
// username – Username used to log into the server.
// deviceId: DeviceId for the device (not validated by server)
// deviceType: Type of device (not validated by server)
// cmd: The actual command being sent across (Provision in this case)

POST https://mail.example.com/Microsoft-Server-ActiveSync?User=username&DeviceId=123412341234&DeviceType=Android&Cmd=Provision HTTP/1.1

// Set the user-agent
User-Agent: Android

// Authorization: This is the text Basic followed by a
// base64 encode of the string DOMAIN\USERNAME:PASSWORD.
// Replace with appropriate values.
Authorization: Basic RE9NQUlOXFVTRVJOQU1FOlBBU1NXT1JE

// Set the content-length to the length of the WBXML being sent (more on this in a bit)
Content-Length: FIXME

// Indicate to the Exchange server that we are sending
// WBXML encoded content.
Content-Type: application/vnd.ms-sync.wbxml

// Identifies the protocol version the client (we) support
// NOTE: This cannot be higher than the highest ActiveSync protocol
// version supported by the server. See my Options primer
// for details.
// Also I would recommend setting this to 12.1, because some Exchange
// 2010 requires servers (v14.1) require 14.1 clients to send several
// optional fields (yep you read that right). Setting this to 12.1
// makes your life a wee bit easier.

MS-ASProtocolVersion: 12.1

// English language
Accept-Language: en-US

// Hostname the request is being sent to
Host: mail.example.com

// Set the PolicyKey to zero indicating to the server
// That you do not currently have a policy key
X-MS-PolicyKey: 0

Body

// Send the following XML string to the server.
// Note that the XML below has to be encoded
// into WBXML before sending it across to the
// Exchange server. More on this in a bit.
// The policyType should be set to
// MS-EAS-Provisioning-WBXML if the activeSync version greater
/ than or equal to 12.0, MS-WAP-Provisioning-XML otherwise

<?xml version="1.0" encoding="utf-8"?>
<Provision xmlns="Provision:">
	<Policies>
		<Policy>
			<!-- If ActiveSync Version >= 12.0 -->
			<PolicyType>MS-EAS-Provisioning-WBXML</PolicyType>
			<!-- If ActiveSync Version < 12.0 -->
			<PolicyType>MS-WAP-Provisioning-XML</PolicyType>
		</Policy>
	</Policies>
</Provision>

Now the XML in the body above has to be encoded into WBXML, before it can be sent across to the server. This is true for all ActiveSync commands that have a body. I wrote a Java implementation of a WBXML encoder and decoder for my app, and you can find the source code here. The source code is based on a WBXML parser I found in the k9mail. I modified the source to add support for International languages.

Step 2: Server responds to client request with security policy and temporary policyKey

Once the request above is sent to the server, you should get a response that looks somewhat like this. Again the XML returned from the server is encoded in WBXML. It is the client’s responsibility to decode this WBXML and make sense of it.

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Length: 1069
Content-Type: application/vnd.ms-sync.wbxml
Server: Microsoft-IIS/7.5
MS-Server-ActiveSync: 8.3
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
Cache-Control: private
Date: Mon, 01 Feb 2011 21:14:17 GMT

<?xml version="1.0" encoding="utf-8"?>
<Provision xmlns="Provision">
<Status>1</Status>
<Policies>
<Policy>
<PolicyType>MS-EAS-Provisioning-WBXML</PolicyType>
<Status>1</Status>
<PolicyKey>2152355410</PolicyKey>
<Data>
	<EASProvisionDoc>
		<DevicePasswordEnabled>0</DevicePasswordEnabled>
		<AlphanumericDevicePasswordRequired>0</AlphanumericDevicePasswordRequired>
		<PasswordRecoveryEnabled>0</PasswordRecoveryEnabled>
		<DeviceEncryptionEnabled>0</DeviceEncryptionEnabled>
		<AttachmentsEnabled>1</AttachmentsEnabled>
		<MinDevicePasswordLength/>
		<MaxInactivityTimeDeviceLock/>
		<MaxDevicePasswordFailedAttempts/>
		<MaxAttachmentSize/>
		<AllowSimpleDevicePassword>0</AllowSimpleDevicePassword>
		<DevicePasswordExpiration/>
		<DevicePasswordHistory>0</DevicePasswordHistory>
		<AllowStorageCard>1</AllowStorageCard>
		<AllowCamera>1</AllowCamera>
		<RequireDeviceEncryption>0</RequireDeviceEncryption>
		<AllowUnsignedApplications>1</AllowUnsignedApplications>
		<AllowUnsignedInstallationPackages>1</AllowUnsignedInstallationPackages>
		<MinDevicePasswordComplexCharacters>3</MinDevicePasswordComplexCharacters>
		<AllowWiFi>1</AllowWiFi>
		<AllowTextMessaging>1</AllowTextMessaging>
		<AllowPOPIMAPEmail>1</AllowPOPIMAPEmail>
		<AllowBluetooth>2</AllowBluetooth>
		<AllowIrDA>1</AllowIrDA>
		<RequireManualSyncWhenRoaming>1</RequireManualSyncWhenRoaming>
		<AllowDesktopSync>1</AllowDesktopSync>
		<MaxCalendarAgeFilter>0</MaxCalendarAgeFilter>
		<AllowHTMLEmail>1</AllowHTMLEmail>
		<MaxEmailAgeFilter>0</MaxEmailAgeFilter>
		<MaxEmailBodyTruncationSize>-1</MaxEmailBodyTruncationSize>
		<MaxEmailHTMLBodyTruncationSize>-1</MaxEmailHTMLBodyTruncationSize>
		<RequireSignedSMIMEMessages>0</RequireSignedSMIMEMessages>
		<RequireEncryptedSMIMEMessages>0</RequireEncryptedSMIMEMessages>
		<RequireSignedSMIMEAlgorithm>0</RequireSignedSMIMEAlgorithm>
		<RequireEncryptionSMIMEAlgorithm>0</RequireEncryptionSMIMEAlgorithm>
		<AllowSMIMEEncryptionAlgorithmNegotiation>2</AllowSMIMEEncryptionAlgorithmNegotiation>
		<AllowSMIMESoftCerts>1</AllowSMIMESoftCerts>
		<AllowBrowser>1</AllowBrowser>
		<AllowConsumerEmail>1</AllowConsumerEmail>
		<AllowRemoteDesktop>1</AllowRemoteDesktop>
		<AllowInternetSharing>1</AllowInternetSharing>
		<UnapprovedInROMApplicationList/>
		<ApprovedApplicationList/>
	</EASProvisionDoc>
</Data>
</Policy>
</Policies>
</Provision>

The 200 response code indicates a success. The XML returned from the server contains the security policy that the server would like the client to implement. Once the client receives this security policy, it needs to implement the security policy indicated in the XML, and then acknowledge receipt of the security policy. Note that the policyKey (2152355410) returned by the server in the response is temporary and needs to be sent to the server in Step 3 (acknowledgement).

Step 3: Client acknowledges receipt and application of security policy

The client should now acknowledge the security policy and its application by using the temporary policyKey obtained in Step 2.

POST https://mail.example.com/Microsoft-Server-ActiveSync?User=username&DeviceId=123412341234&DeviceType=Android&Cmd=Provision HTTP/1.1
User-Agent: Android
Authorization: Basic RE9NQUlOXFVTRVJOQU1FOlBBU1NXT1JE
Content-Length: FIXME
Content-Type: application/vnd.ms-sync.wbxml
MS-ASProtocolVersion: 12.1
Accept-Language: en-US
Host: mail.example.com
X-MS-PolicyKey: 2152355410

<?xml version="1.0" encoding="utf-8"?>
<Provision xmlns="Provision:">
  <Policies>
    <Policy>
      <PolicyType>MS-EAS-Provisioning-WBXML</PolicyType>
      <PolicyKey>2152355410</PolicyKey>
      <Status>1</Status>
    </Policy>
  </Policies>
</Provision>


Step 4: Server responds with final policyKey

At this point the server will respond with the “final” policyKey which the client then uses in the X-MS-PolicyKey header of all successive command requests to the server.

HTTP/1.1 200 OK
Connection: Keep-Alive
Content-Length: 1069
Content-Type: application/vnd.ms-sync.wbxml
Server: Microsoft-IIS/7.5
MS-Server-ActiveSync: 8.3
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
Cache-Control: private
Date: Mon, 01 Feb 2011 21:15:17 GMT

<?xml version="1.0" encoding="utf-8"?>
<Provision xmlns="Provision:">
  <Status>1</Status>
    <Policies>
       <Policy>
           <PolicyType>MS-EAS-Provisioning-WBXML</PolicyType>
           <Status>1</Status>
           <PolicyKey>12432432244</PolicyKey>
       </Policy>
     </Policies>
</Provision>

A word of caution here. I have seen cases where a server processes a few client requests that contain the final policyKey obtained using the method above, and then start sending down a 449 or a 142 error code. This implies that the client needs to acknowledge the policy settings again. So make sure you always check for 142 and 449 error codes even if you have accepted the policy settings once and received a final policyKey.

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