In this blog post we are going to have a look at how you can use the Azure Arc provided Azure Active Directory (Azure AD) managed identity (MSI) to authenticate in Azure PowerShell on your on-premises Linux and Windows Server machines.

The moment you want to run some automation directly on your servers, you often end up in a scenario where you need some credentials to run your PowerShell script. Now the issue with that is that you need to store or get your credentials from somewhere and that can be an issue. Luckly, Azure Arc provides you with an Azure Active Directory Managed Identity which can be used for that.

Azure PowerShell allows you an uncomplicated way to login using that managed identity.

Prerequisites

• On Windows, you must be a member of the local Administrators group or the Hybrid Agent Extension Applications group.
• On Linux, you must be a member of the himds group.
• I connected my servers to Azure using Azure Arc enabled servers and installed the Azure connected machine agent.

• You are a member of the Owner group in the subscription or resource group, in order to perform required resource creation and role management steps.

• Have Azure PowerShell installed, depending on what you are planning to use.

Get an access token using REST API

For an Azure Arc-enabled Windows server, using PowerShell, you invoke the web request to get the token from the local host in the specific port. Specify the request using the IP address or the environmental variable IDENTITY_ENDPOINT.

$apiVersion = "2020-06-01"
$resource = "https://management.azure.com/"
$endpoint = "{0}?resource={1}&api-version={2}" -f $env:IDENTITY_ENDPOINT,$resource,$apiVersion
$secretFile = ""
try
{
    Invoke-WebRequest -Method GET -Uri $endpoint -Headers @{Metadata='True'} -UseBasicParsing
}
catch
{
    $wwwAuthHeader = $_.Exception.Response.Headers["WWW-Authenticate"]
    if ($wwwAuthHeader -match "Basic realm=.+")
    {
        $secretFile = ($wwwAuthHeader -split "Basic realm=")[1]
    }
}
Write-Host "Secret file path: " $secretFile`n
$secret = cat -Raw $secretFile
$response = Invoke-WebRequest -Method GET -Uri $endpoint -Headers @{Metadata='True'; Authorization="Basic $secret"} -UseBasicParsing
if ($response)
{
    $token = (ConvertFrom-Json -InputObject $response.Content).access_token
    Write-Host "Access token: " $token
}

For an Azure Arc-enabled Linux server, using Bash, you invoke the web request to get the token from the local host in the specific port. Specify the following request using the IP address or the environmental variable IDENTITY_ENDPOINT. To complete this step, you need an SSH client.

ChallengeTokenPath=$(curl -s -D - -H Metadata:true "http://127.0.0.1:40342/metadata/identity/oauth2/token?api-version=2019-11-01&resource=https%3A%2F%2Fmanagement.azure.com" | grep Www-Authenticate | cut -d "=" -f 2 | tr -d "[:cntrl:]")
ChallengeToken=$(cat $ChallengeTokenPath)
if [ $? -ne 0 ]; then
    echo "Could not retrieve challenge token, double check that this command is run with root privileges."
else
    curl -s -H Metadata:true -H "Authorization: Basic $ChallengeToken" "http://127.0.0.1:40342/metadata/identity/oauth2/token?api-version=2019-11-01&resource=https%3A%2F%2Fmanagement.azure.com"
fi

You can learn more about this on Microsoft Learn.

Login with Azure PowerShell on Azure Arc enabled server using Managed Identity

To login with your managed identity using Azure PowerShell, run the following command:

Connect-AzAccount -Identity

Now you have access to the resources your Azure AD managed identity (MSI) on your Azure Arc-enabled server has permissions to.

Conclusion

I hope this post is helpful to build some automation with Azure PowerShell on your on-premises or multi-cloud servers with Azure Arc. Let me know if you have any questions in the comments below.