Use Azure PowerShell to create a service principal with a certificate

When you have an app or script that needs to access resources, you can set up an identity for the app and authenticate the app with its own credentials. This identity is known as a service principal. This approach enables you to:

• Assign permissions to the app identity that are different than your own permissions. Typically, these permissions are restricted to exactly what the app needs to do.
• Use a certificate for authentication when executing an unattended script.

This article shows you how to create a service principal that authenticates with a certificate. To set up a service principal with password, see Create an Azure service principal with Azure PowerShell.

You must have the latest version of PowerShell for this article.

Required permissions

To complete this article, you must have sufficient permissions in both your Microsoft Entra ID and Azure subscription. Specifically, you must be able to create an app in Microsoft Entra ID, and assign the service principal to a role.

The easiest way to check whether your account has adequate permissions is through the Microsoft Entra admin center.

Assign the application to a role

To access resources in your subscription, you must assign the application to a role. Decide which role offers the right permissions for the application. To learn about the available roles, see Azure built-in roles.

You can set the scope at the level of the subscription, resource group, or resource. Permissions are inherited to lower levels of scope. For example, adding an application to the Reader role for a resource group means it can read the resource group and any resources it contains. To allow the application to execute actions like reboot, start and stop instances, select the Contributor role.

Create service principal with self-signed certificate

The following example covers a simple scenario. It uses New-​AzAD​Service​Principal to create a service principal with a self-signed certificate, and uses New-AzRoleAssignment to assign the Reader role to the service principal. The role assignment is scoped to your currently selected Azure subscription. To select a different subscription, use Set-AzContext.

$cert = New-SelfSignedCertificate -CertStoreLocation "cert:\CurrentUser\My" `
  -Subject "CN=exampleappScriptCert" `
  -KeySpec KeyExchange
$keyValue = [System.Convert]::ToBase64String($cert.GetRawCertData())

$sp = New-AzADServicePrincipal -DisplayName exampleapp `
  -CertValue $keyValue `
  -EndDate $cert.NotAfter `
  -StartDate $cert.NotBefore
Sleep 20
New-AzRoleAssignment -RoleDefinitionName Reader -ServicePrincipalName $sp.AppId

The example sleeps for 20 seconds to allow some time for the new service principal to propagate throughout Microsoft Entra ID. If your script doesn't wait long enough, you'll see an error stating: "Principal {ID} doesn't exist in the directory {DIR-ID}." To resolve this error, wait a moment then run the New-AzRoleAssignment command again.

You can scope the role assignment to a specific resource group by using the ResourceGroupName parameter. You can scope to a specific resource by also using the ResourceType and ResourceName parameters.

If you do not have Windows 10 or Windows Server 2016, download the New-SelfSignedCertificateEx cmdlet from PKI Solutions. Extract its contents and import the cmdlet you need.

# Only run if you could not use New-SelfSignedCertificate
Import-Module -Name c:\ExtractedModule\New-SelfSignedCertificateEx.ps1

In the script, substitute the following two lines to generate the certificate.

New-SelfSignedCertificateEx -StoreLocation CurrentUser `
  -Subject "CN=exampleapp" `
  -KeySpec "Exchange" `
  -FriendlyName "exampleapp"
$cert = Get-ChildItem -path Cert:\CurrentUser\my | where {$PSitem.Subject -eq 'CN=exampleapp' }

Provide certificate through automated PowerShell script

Whenever you sign in as a service principal, provide the tenant ID of the directory for your AD app. A tenant is an instance of Microsoft Entra ID.

$TenantId = (Get-AzSubscription -SubscriptionName "Contoso Default").TenantId
$ApplicationId = (Get-AzADApplication -DisplayNameStartWith exampleapp).AppId

$Thumbprint = (Get-ChildItem cert:\CurrentUser\My\ | Where-Object {$_.Subject -eq "CN=exampleappScriptCert" }).Thumbprint
Connect-AzAccount -Environment AzureChinaCloud -ServicePrincipal `
  -CertificateThumbprint $Thumbprint `
  -ApplicationId $ApplicationId `
  -TenantId $TenantId

Create service principal with certificate from Certificate Authority

The following example uses a certificate issued from a Certificate Authority to create service principal. The assignment is scoped to the specified Azure subscription. It adds the service principal to the Reader role. If an error occurs during the role assignment, it retries the assignment.

Param (
 [Parameter(Mandatory=$true)]
 [String] $ApplicationDisplayName,

 [Parameter(Mandatory=$true)]
 [String] $SubscriptionId,

 [Parameter(Mandatory=$true)]
 [String] $CertPath,

 [Parameter(Mandatory=$true)]
 [String] $CertPlainPassword
 )

 Connect-AzAccount -Environment AzureChinaCloud
 Import-Module Az.Resources
 Set-AzContext -Subscription $SubscriptionId

 $CertPassword = ConvertTo-SecureString $CertPlainPassword -AsPlainText -Force

 $PFXCert = New-Object -TypeName System.Security.Cryptography.X509Certificates.X509Certificate2 -ArgumentList @($CertPath, $CertPassword)
 $KeyValue = [System.Convert]::ToBase64String($PFXCert.GetRawCertData())

 $ServicePrincipal = New-AzADServicePrincipal -DisplayName $ApplicationDisplayName
 New-AzADSpCredential -ObjectId $ServicePrincipal.Id -CertValue $KeyValue -StartDate $PFXCert.NotBefore -EndDate $PFXCert.NotAfter
 Get-AzADServicePrincipal -ObjectId $ServicePrincipal.Id 

 $NewRole = $null
 $Retries = 0;
 While ($NewRole -eq $null -and $Retries -le 6)
 {
    # Sleep here for a few seconds to allow the service principal application to become active (should only take a couple of seconds normally)
    Sleep 15
    New-AzRoleAssignment -RoleDefinitionName Reader -ServicePrincipalName $ServicePrincipal.AppId | Write-Verbose -ErrorAction SilentlyContinue
    $NewRole = Get-AzRoleAssignment -ObjectId $ServicePrincipal.Id -ErrorAction SilentlyContinue
    $Retries++;
 }

 $NewRole

Provide certificate through automated PowerShell script

Whenever you sign in as a service principal, provide the tenant ID of the directory for your AD app. A tenant is an instance of Microsoft Entra ID.

Param (

 [Parameter(Mandatory=$true)]
 [String] $CertPath,

 [Parameter(Mandatory=$true)]
 [String] $CertPlainPassword,

 [Parameter(Mandatory=$true)]
 [String] $ApplicationId,

 [Parameter(Mandatory=$true)]
 [String] $TenantId
 )

 $CertPassword = ConvertTo-SecureString $CertPlainPassword -AsPlainText -Force
 $PFXCert = New-Object `
  -TypeName System.Security.Cryptography.X509Certificates.X509Certificate2 `
  -ArgumentList @($CertPath, $CertPassword)
 $Thumbprint = $PFXCert.Thumbprint

 Connect-AzAccount -Environment AzureChinaCloud -ServicePrincipal `
  -CertificateThumbprint $Thumbprint `
  -ApplicationId $ApplicationId `
  -TenantId $TenantId

The application ID and tenant ID aren't sensitive, so you can embed them directly in your script. If you need to retrieve the tenant ID, use:

(Get-AzSubscription -SubscriptionName "Contoso Default").TenantId

If you need to retrieve the application ID, use:

(Get-AzADApplication -DisplayNameStartWith {display-name}).AppId

Change credentials

To change the credentials for an AD app, either because of a security compromise or a credential expiration, use the Remove-AzADAppCredential and New-AzADAppCredential cmdlets.

To remove all the credentials for an application, use:

Get-AzADApplication -DisplayName exampleapp | Remove-AzADAppCredential

To add a certificate value, create a self-signed certificate as shown in this article. Then, use:

Get-AzADApplication -DisplayName exampleapp | New-AzADAppCredential `
  -CertValue $keyValue `
  -EndDate $cert.NotAfter `
  -StartDate $cert.NotBefore

Debug

You may get the following errors when creating a service principal:

• "Authentication_Unauthorized" or "No subscription found in the context." - You see this error when your account doesn't have the required permissions on the Microsoft Entra ID to register an app. Typically, you see this error when only admin users in your Microsoft Entra ID can register apps, and your account isn't an admin. Ask your administrator to either assign you to an administrator role, or to enable users to register apps.

• Your account "does not have authorization to perform action 'Microsoft.Authorization/roleAssignments/write' over scope '/subscriptions/{guid}'." - You see this error when your account doesn't have sufficient permissions to assign a role to an identity. Ask your subscription administrator to add you to User Access Administrator role.

Next steps

• To set up a service principal with password, see Create an Azure service principal with Azure PowerShell or Create an Azure service principal with Azure CLI.
• For a more detailed explanation of applications and service principals, see Application Objects and Service Principal Objects.
• For more information about Microsoft Entra authentication, see Authentication Scenarios for Microsoft Entra ID.
• For information about working with app registrations by using Microsoft Graph, see the Applications API reference.