Set extension attribute for a device.

Set-MgDeviceExtensionAttribute.ps1

<#PSScriptInfo
.VERSION 1.0.0
.GUID 380c73f8-ef67-4aeb-ae6b-2f5e563fabb8
.AUTHOR Julian Pawlowski
.COMPANYNAME Julian Pawlowski
.COPYRIGHT © 2024 Julian Pawlowski
.TAGS
.LICENSEURI https://opensource.org/license/MIT
.PROJECTURI https://gist.github.com/jpawlowski/d9e7cb61a36a4a22a69a935657e77335
.ICONURI
.EXTERNALMODULEDEPENDENCIES 'Microsoft.Graph.Authentication'
.REQUIREDSCRIPTS
.EXTERNALSCRIPTDEPENDENCIES
.RELEASENOTES
    Version 1.0.0 (2024-06-11)
    - Initial release.
#>

<#
.SYNOPSIS
    Set extension attribute for a device.

.DESCRIPTION
    Set extension attribute for a device.

.PARAMETER DeviceId
    The ID or display name of the device.

.PARAMETER ExtensionAttribute
    The extension attribute number (1-15).

.PARAMETER Value
    The value to set.
#>

#Requires -Modules @{ ModuleName = 'Microsoft.Graph.Authentication'; ModuleVersion = '2.0.0'}

[CmdletBinding()]
param(
    [Parameter(Mandatory = $true)]
    [string]$DeviceId,

    [Parameter(Mandatory = $true)]
    [ValidateRange(1, 15)]
    [int]$ExtensionAttribute,

    [Parameter(Mandatory = $true)]
    [string]$Value
)

if (-not (Get-MgContext)) {
    $params = @{
        Scopes       = @(
            'Device.ReadWrite.All'
        )
        ContextScope = 'Process'
        NoWelcome    = $true
        ErrorAction  = 'Stop'
    }
    Connect-MgGraph @params
}

if ($DeviceId -notmatch '^[0-9a-f]{8}-([0-9a-f]{4}-){3}[0-9a-f]{12}$') {
    $DeviceId = (Invoke-MgGraphRequest -Uri "https://graph.microsoft.com/v1.0/devices?`$filter=displayName eq '$DeviceId'" -ErrorAction 'Stop').value.id

    if (-not $DeviceId) {
        Write-Error 'Device not found' -ErrorAction 'Stop'
        exit 1
    }    
}

$params = @{
    Uri         = "https://graph.microsoft.com/v1.0/devices/$DeviceId"
    Method      = 'PATCH'
    Body        = @{
        extensionAttributes = @{
            "extensionAttribute$ExtensionAttribute" = $Value
        }
    }
    ErrorAction = 'Stop'
}
Invoke-MgGraphRequest @params