UpdateClientSecret.ps1

Param(
    [Parameter(Mandatory=$True)]
    $AppPrincipalId,

    [Parameter(Mandatory=$True)]
    $TenantId,

    [string]$ClientSecret
)

try
{
    $ErrorActionPreference = "Stop"

    [System.Guid]::Parse($AppPrincipalId) | Out-Null
    [System.Guid]::Parse($TenantId) | Out-Null

    if([string]::IsNullOrWhiteSpace($ClientSecret)) {
        $bytes = New-Object Byte[] 32
        $rand = [System.Security.Cryptography.RandomNumberGenerator]::Create()
        $rand.GetBytes($bytes)
        $rand.Dispose()
        $newClientSecret = [System.Convert]::ToBase64String($bytes)
    }
    else {        
        $newClientSecret = $ClientSecret
    }

    
    $dtStart = [System.DateTime]::Now.AddDays(-1)
    $dtEnd = $dtStart.AddYears(3)

    Write-Host -f Green "`nUpdating app $AppPrincipalId in tenant $TenantId"
    
    [System.Threading.Thread]::Sleep(1000)

    Write-Host -f Gray "`nConnecting to Azure AD"
    Connect-MsolService
    
    # Recreate the service principal for instant update
    Write-Host -f Gray "`nUpdating service principal"
    $servicePrincipal = Get-MsolServicePrincipal -TenantId $TenantId -AppPrincipalId $AppPrincipalId    
    Remove-MsolServicePrincipal -TenantId $TenantId -AppPrincipalId $AppPrincipalId
    New-MsolServicePrincipal -TenantId $TenantId -AppPrincipalId $AppPrincipalId -DisplayName $servicePrincipal.DisplayName -ServicePrincipalNames $servicePrincipal.ServicePrincipalNames -AccountEnabled:$true -Addresses $servicePrincipal.Addresses

    # Remove the auto-generated key
    $keys = @()
    Get-MsolServicePrincipalCredential -TenantId $TenantId -AppPrincipalID $AppPrincipalId -ReturnKeyValues:$true | ForEach-Object {
        $keys += $_.KeyId
    }
    Remove-MsolServicePrincipalCredential -TenantId $TenantId -AppPrincipalID $AppPrincipalId -KeyIds $keys

    Write-Host -f Gray "`nCreating new service principal credentials"
    New-MsolServicePrincipalCredential -TenantId $TenantId -AppPrincipalId $AppPrincipalId -Type Symmetric -Usage Sign -Value $newClientSecret -StartDate $dtStart -EndDate $dtEnd
    New-MsolServicePrincipalCredential -TenantId $TenantId -AppPrincipalId $AppPrincipalId -Type Symmetric -Usage Verify -Value $newClientSecret -StartDate $dtStart -EndDate $dtEnd
    New-MsolServicePrincipalCredential -TenantId $TenantId -AppPrincipalId $AppPrincipalId -Type Password -Usage Verify -Value $newClientSecret -StartDate $dtStart -EndDate $dtEnd

    Write-Host -f Green "`nClient secret created:"
    Write-Host "$newClientSecret`n"
}
catch
{
    Write-Error $_
}