migrating-from-azuread-and-msonline-to-microsoft-graph-powershell-snippet-16.ps1

function Register-MyGraphApp {
    [CmdletBinding()]
    param(
        [Parameter(Mandatory)]
        [ValidateNotNullOrEmpty()]
        [string]
        $DisplayName
    )


    $requiredModules = @("Az.Accounts", "Az.Resources")
    foreach ($module in $requiredModules) {
        $isLoaded = Get-Module -Name $module
        if ($isLoaded) {
            Write-Verbose -Message "$($module) module is loaded."
        } else {
            Write-Error -Message "$($module) module is not loaded, please install by 'Install-Module $($module)'."
        }
    }

    $apiId = "00000003-0000-0000-c000-000000000000" # Microsoft Graph
    $requiredPermissions = @(
        "a154be20-db9c-4678-8ab7-66f6cc099a59", # (User.Read.All)
        "aec28ec7-4d02-4e8c-b864-50163aea77eb" # (UserAuthenticationMethod.Read.All)
    )

    
    $app = Get-AzADApplication -DisplayName $DisplayName
    if (-not ($app)) {
        Write-Verbose -Message "Azure Application was not found. Creating..."
        $params = @{
            DisplayName = $displayName
            SignInAudience = "AzureADMyOrg"
            IsFallbackPublicClient = $true
        }
        $app = New-AzADApplication @params
        Write-Verbose -Message "Azure Application created: $($app.AppId)"
    } else {
        Write-Verbose -Message ("App Registration {0} already exists" -f $DisplayName)
    }

    $spForApp = Get-AzADServicePrincipal -ApplicationId $app.AppId
    if (-not ($spForApp)) {
        $spForApp = New-AzADServicePrincipal -ApplicationId $app.AppId
        foreach ($permission in $requiredPermissions) {
            Add-AzADAppPermission -ObjectId $app.Id -ApiId $apiId -PermissionId $permission
        }
        Write-Verbose -Message "Azure Service Principal created: $($spForApp.Id)"
    } else {
        Write-Verbose -Message "Service Principal already exists"
    }

    [PSCustomObject]@{
        ClientId               = $app.AppId
        TenantId               = (Get-AzContext).Tenant.Id
    }
}