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Assign a managed identity access to an application role using Azure CLI

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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.

Note

The tokens which your application receives are cached by the underlying infrastructure, which means that any changes to the managed identity's roles can take significant time to take effect. For more information, see Limitation of using managed identities for authorization.

In this article, you learn how to assign a managed identity to an application role exposed by another application using Azure CLI.

Prerequisites

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

  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 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}"

oidForMI=$(az resource show --ids $resourceIdWithManagedIdentity --query "identity.principalId" -o tsv | tr -d '[:space:]')
echo "object id for managed identity is: $oidForMI"

    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 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}"

oidForMI=$(az resource show --id $userManagedIdentityResourceId --query "properties.principalId" -o tsv | tr -d '[:space:]')
echo "object id for managed identity is: $oidForMI"

  3. Create a new application registration to represent the service that your managed identity will 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.

  4. Find the object ID of the service application's service principal. You can find this using the Azure portal. Go to Microsoft Entra ID and open the Enterprise applications page, then find the application and look for the Object ID. You can also find the service principal's object ID by its display name using the following script:

    appName="{name for your application}"
serverSPOID=$(az ad sp list --filter "displayName eq '$appName'" --query '[0].id' -o tsv | tr -d '[:space:]')
echo "object id for server service principal is: $serverSPOID"

    Note

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

    Alternatively you can find the Object ID by the unique Application ID for your application registration:

    appID="{application id for your application}"
serverSPOID=$(az ad sp list --filter "appId eq '$appID'" --query '[0].id' -o tsv | tr -d '[:space:]')
echo "object id for server service principal is: $serverSPOID"

  5. Add an app role to the application you created in step 3. You can create the role using the Azure portal or using Microsoft Graph. For example, you could add an app role like this:

    {
    "allowedMemberTypes": [
        "Application"
    ],
    "displayName": "Read data from MyApi",
    "id": "0566419e-bb95-4d9d-a4f8-ed9a0f147fa6",
    "isEnabled": true,
    "description": "Allow the application to read data as itself.",
    "value": "MyApi.Read.All"
}

  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 step 2.
    • 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 0566419e-bb95-4d9d-a4f8-ed9a0f147fa6.

    Execute the following script to add the role assignment. Note that this functionality is not directly exposed on the Azure CLI and that a REST command is used here instead:

    roleguid="0566419e-bb95-4d9d-a4f8-ed9a0f147fa6"
az rest -m POST -u https://graph.microsoft.com/v1.0/servicePrincipals/$oidForMI/appRoleAssignments -b "{\"principalId\": \"$oidForMI\", \"resourceId\": \"$serverSPOID\",\"appRoleId\": \"$roleguid\"}"

Next steps