React to MEM Logs using Event Hubs and Azure Functions

Example: Convert User-Driven provisioned Autopilot Devices to Shared Devices

I’ve got an interesting challenge from one of my customers.
Long story short, we have hybrid ad joined devices (for no really good reason, I know 😉 ), but only “User Driven Provisioning” via Windows Autopilot is available (at the moment).
But mobile devices get shared regularly for weekend tasks, the customer wants to allow every user to use the company portal on these devices.
The only way to accomplish this at the moment is to remove the primary user from the device in the MEM Admin Portal, because this will “convert” the device into a shared device.
So he wants me to automate this when a new device gets enrolled in intune via Windows Autopilot.

In the past, I’ve often used Azure Monitor with Alerts and Runbooks to perform tasks like this.
But since I’ve dug a little bit into Azure Functions in my last project, I decided to go with an alternative approach this time. (Because Azure Functions are so damn awesome and a shout-out to Laura Kokkarinen, her blog post helps me a lot: Link )

So lets start, that’s the plan:

  1. Logstreaming MEM operational logs and looking for a specific “event”.
  2. Redirect formatted output of a specific event to a new logstream
  3. The redirected event triggers Azure Functions via binding
  4. Azure Function calls Microsoft Graph with a token from the Managed Identity endpoint (that’s by far the coolest part)

Create the necessary Event Hubs

We create two Event Hubs in our new namespace, one for operational logs and one for the filtered enrollment events (we will get into that later).

Forward MEM Operational Log to Event Hub

Return to the MEM Admin Portal and configure log forwarding.

Note: Now is a good time to enroll a test device, so you have some log entries to play with.

Configure Azure Stream Analytics Job

Let’s take a look at the logstream. We navigate back to our event hub namespace and open our previously selected event hub.

We save the query as a stream analytics job.
We add output to our “Analytics Job”.
Don’t forget to start the job (unfortunately discovered after 2 hours of troubleshooting :-))
Note: Again, now is another good time to enroll a device, so we can validate if entries are received by our event hubs.

Create Azure Function and bind to Event Hub

We now create a new Azure Function App with your favorite runtime stack. I usually go with Powershell and my demo code is also written in Powershell (so if you want simple copy and paste –> select Powershell Core).
The rest of the settings are good by default, and the serverless plan is the most beaty one :-). Application Insights give us a historical view.

Next we create our first function in our new Function App and bind it with our “newenrolleddevice” event hub.
Click create and the portal brings us to our new function, where we go to the “Code + Test” section and enter the following code and click “Save”.

param($eventHubMessages, $TriggerMetadata)

# Write-Host "PowerShell event hub trigger function called for message array: $eventHubMessages"

$eventHubMessages | ForEach-Object {

    # get Intune device id
    $jsonOut = $_ | convertto-json
    Write-Host "Processing event: $jsonOut"

    $deviceID = $_.properties.IntuneDeviceId
    Write-Host "DeviceID: $deviceID"

    try {
        # request accesstoken from managed identity
        Write-Host "Trying to get authentication token from managed identity."
        $authToken = Receive-MyMsiGraphToken

        #Invoke REST call to Graph API
        Write-Host "Call Microsoft Graph to remove primary user from device."
        Remove-MyPrimaryUser -IntuneDeviceID $deviceID -AuthToken $authToken
    }
    catch {
        Write-Error $_
    }
}

As you might see, I use 2 helper functions in this example. “Receive-MyMsiGraphToken” and “Remove-MyPrimaryUser”, we add this function to the “profile.ps1”. The “profile.ps1” file loads every time the function does a cold start.

We append the following code to our “profile.ps1” file.
function Receive-MyMsiGraphToken {
    $Scope = "https://graph.microsoft.com/"
    $tokenAuthUri = $env:IDENTITY_ENDPOINT + "?resource=$Scope&api-version=2019-08-01"

    $splatt = @{
        Method = "Get"
        Uri = $tokenAuthUri
        UseBasicParsing = $true
        Headers = @{
            "X-IDENTITY-HEADER" = "$env:IDENTITY_HEADER"
        }
    }
    $response = Invoke-RestMethod @splatt
    $accessToken = $response.access_token

    if ($accessToken) {
        return $accessToken
    }
    else {
        throw "Could not receive auth token for msgraph, maybe managed Identity is not enabled for this function"
    }
}
function Remove-MyPrimaryUser {
    param (
        $AuthToken,
        $IntuneDeviceID
    )
    $splatt = @{
        Method = "DELETE"
        Uri = "https://graph.microsoft.com/beta/deviceManagement/managedDevices('$IntuneDeviceID')/users/`$ref"
        UseBasicParsing = $true
        ContentType = "application/json"
        # ResponseHeadersVariable = "RES"
        Headers = @{
            'Content-Type'='application/json'
            'Authorization'= 'Bearer ' +  $AuthToken
        }
    }
    $result = (Invoke-RestMethod @splatt).value

    if ([string]::IsNullOrEmpty($result)) {
        return $true
    }
    else {
        throw "Removing primary user from device ('$IntuneDeviceID') failed"
    }
}

Add MS Graph permissions to the Azure Function App

Now we have everything in place, for our final part. We have to add some permissions to our Azure Function App.

We enable the managed identity for our function app and we copy the object ID to our clipboard because we need it in the next step.
# replace with your managed identity object ID
$miObjectID = "place your object id here"

# MS Graph app ID
$appId = "00000003-0000-0000-c000-000000000000"

# replace with the API permissions required by your app
$permissionsToAdd = @(
    "DeviceManagementManagedDevices.ReadWrite.All"
)

Connect-AzureAD

$app = Get-AzureADServicePrincipal -Filter "AppId eq '$appId'"

foreach ($permission in $permissionsToAdd) {
    $role = $app.AppRoles | Where-Object Value -Like $permission | Select-Object -First 1
    New-AzureADServiceAppRoleAssignment -Id $role.Id -ObjectId $miObjectID -PrincipalId $miObjectID -ResourceId $app.ObjectId
}


# Restart app after changing permission

Try it out

We reset and reenroll our test device/VM and take a look. After some time, we should see the message received by our “newenrolleddevice” logstream.

And some “success” messages in our function monitoring

Some final words

  • This is only an example, so please feel free to select different tiers and plans to meet your needs
  • Why redirecting into an new Event Hub? For demonstration purposes only, if you use this method in an environment with thousands of clients, you can easily reduce the number of times your function is invoked.
  • The possibilities are basically endless; tagging based on geolocation, joining groups based on properties, which are not supported at the moment, etc…

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