Assign an application role to a managed identity using PowerShell

Managed identities for Azure resources provide Azure services with an identity in Microsoft Entra ID. They work without needing credentials in your code. Azure services use this identity to authenticate to services that support Microsoft Entra authentication. Application roles provide a form of role-based access control, and allow a service to implement authorization rules.

In this article, you'll learn how to assign a managed identity to an application role exposed by another application using the Microsoft Graph PowerShell SDK or Azure CLI.

Prerequisites

• If you're unfamiliar with managed identities for Azure resources, see Managed identity for Azure resources overview.
• Review the difference between a system-assigned and user-assigned managed identity.
• If you don't already have an Azure account, sign up for a Trial before continuing.

Assign a managed identity access to another application's app role using PowerShell

Run scripts locally by installing the latest version of the Microsoft Graph PowerShell SDK.

1. Enable managed identity on an Azure resource, such as an Azure VM.

2. Find the object ID of the managed identity's service principal.

   For a system-assigned managed identity, you can find the object ID on the Azure portal on the resource's Identity page. You can also use the following PowerShell script to find the object ID. You'll need the resource ID of the resource you created in step 1, which is available in the Azure portal on the resource's Properties page.

   $resourceIdWithManagedIdentity = '/subscriptions/{my subscription ID}/resourceGroups/{my resource group name}/providers/Microsoft.Compute/virtualMachines/{my virtual machine name}'
   (Get-AzResource -ResourceId $resourceIdWithManagedIdentity).Identity.PrincipalId
   

   For a user-assigned managed identity, you can find the managed identity's object ID on the Azure portal on the resource's Overview page. You can also use the following PowerShell script to find the object ID. You'll need the resource ID of the user-assigned managed identity.

   $userManagedIdentityResourceId = '/subscriptions/{my subscription ID}/resourceGroups/{my resource group name}/providers/Microsoft.ManagedIdentity/userAssignedIdentities/{my managed identity name}'
   (Get-AzResource -ResourceId $userManagedIdentityResourceId).Properties.PrincipalId
   

3. Create a new application registration to represent the service that you want your managed identity to send a request to.

   • If the API or service that exposes the app role grant to the managed identity already has a service principal in your Microsoft Entra tenant, skip this step. For example, in the case that you want to grant the managed identity access to the Microsoft Graph API.

4. Find the object ID of the service application's service principal. You can find this using the Microsoft Entra admin center.

   1. Sign in to the Microsoft Entra admin center.
   2. In the left nav blade, select Entra ID > Enterprise apps. Then find the application and look for the Object ID.
   3. You can also find the service principal's object ID by its display name using the following PowerShell script:

   $serverServicePrincipalObjectId = (Get-MgServicePrincipal -Filter "DisplayName eq '$applicationName'").Id
   

   Note

   Display names for applications aren't unique, so you should verify that you obtain the correct application's service principal.

5. Add an app role to the application you created in the previous step. You can then create the role using the Azure portal.

6. Assign the app role to the managed identity. You'll need the following information to assign the app role:

   • managedIdentityObjectId: the object ID of the managed identity's service principal, which you found in the previous step.

   • serverServicePrincipalObjectId: the object ID of the server application's service principal, which you found in step 4.

   • appRoleId: the ID of the app role exposed by the server app, which you generated in step 5 - in the example, the app role ID is 00000000-0000-0000-0000-000000000000.

   • Execute the following PowerShell command to add the role assignment:

     New-MgServicePrincipalAppRoleAssignment `
         -ServicePrincipalId $serverServicePrincipalObjectId `
         -PrincipalId $managedIdentityObjectId `
         -ResourceId $serverServicePrincipalObjectId `
         -AppRoleId $appRoleId
     

Complete example script

This example script shows you how to assign an Azure web app's managed identity to an app role.

# Install the module.
# Install-Module Microsoft.Graph -Scope CurrentUser

# Your tenant ID (in the Azure portal, under Azure Active Directory > Overview).
$tenantID = '<tenant-id>'

# The name of your web app, which has a managed identity that should be assigned to the server app's app role.
$webAppName = '<web-app-name>'
$resourceGroupName = '<resource-group-name-containing-web-app>'

# The name of the server app that exposes the app role.
$serverApplicationName = '<server-application-name>' # For example, MyApi

# The name of the app role that the managed identity should be assigned to.
$appRoleName = '<app-role-name>' # For example, MyApi.Read.All

# Look up the web app's managed identity's object ID.
$managedIdentityObjectId = (Get-AzWebApp -ResourceGroupName $resourceGroupName -Name $webAppName).identity.principalid

Connect-MgGraph -Environment China -ClientId 'YOUR_CLIENT_ID' -TenantId $tenantId -Scopes 'Application.Read.All','Application.ReadWrite.All','AppRoleAssignment.ReadWrite.All','Directory.AccessAsUser.All','Directory.Read.All','Directory.ReadWrite.All'

# Look up the details about the server app's service principal and app role.
$serverServicePrincipal = (Get-MgServicePrincipal -Filter "DisplayName eq '$serverApplicationName'")
$serverServicePrincipalObjectId = $serverServicePrincipal.Id
$appRoleId = ($serverServicePrincipal.AppRoles | Where-Object {$_.Value -eq $appRoleName }).Id

# Assign the managed identity access to the app role.
New-MgServicePrincipalAppRoleAssignment `
    -ServicePrincipalId $serverServicePrincipalObjectId `
    -PrincipalId $managedIdentityObjectId `
    -ResourceId $serverServicePrincipalObjectId `
    -AppRoleId $appRoleId

Next steps

Managed identity for Azure resources overview