WildCard Certificate for Authentication to API Driven Inbound Provisioning Application

Question

Hi All,

Is it possible to use a wildcard certificate for authenticating to an API-driven inbound provisioning application via a service principal in a PowerShell script?

For example:

Issue to : *acme.corp.uk

1. We will upload the Wildcard Certificate within Service Principal
2. In PowerShell script we will check the thumbprint to authenticate to API app

Thanks,

Vidisha

Answer 1

Hello @Khedkar, Vidisha

To check on this Follow Steps:

[Step 1]: Uploading the Wildcard Certificate to the Service Principal

Yes, it is possible to upload a wildcard certificate to a service principal in Azure AD. The process is the same as uploading a regular certificate. You'll need to convert the certificate to a suitable format (e.g., .pfx or .cer) and upload it to the service principal's credentials.

[Step 2]: Authenticating with PowerShell using the Certificate

You can use the Connect-AzAccount cmdlet (or similar, depending on the specific Azure modules you're using) to authenticate with the service principal using the certificate. Here's a general outline:

# Replace with your actual values

$tenantId = "your_tenant_id"

$appId = "your_app_id"

$certificatePath = "path_to_your_wildcard_certificate.pfx"

$certificatePassword = "your_certificate_password" # If the PFX is password protected

# Import the certificate

$certificate = Get-PfxCertificate -FilePath $certificatePath -Password $certificatePassword

# Connect to Azure using the service principal and certificate

Connect-AzAccount -ServicePrincipal -TenantId $tenantId -ApplicationId $appId -Certificate $certificate

[Step 3]: Verifying the Thumbprint

While not strictly required for authentication (the Connect-AzAccount cmdlet handles the certificate validation), you can verify the thumbprint in your script for added security or validation purposes.

# Get the thumbprint of the certificate

$thumbprint = $certificate.Thumbprint

# Display the thumbprint

Write-Host "Certificate Thumbprint: $thumbprint"

# Example: Compare the thumbprint to an expected value

$expectedThumbprint = "expected_thumbprint_value"

if ($thumbprint -eq $expectedThumbprint) {

    Write-Host "Thumbprint matches the expected value."

} else {

    Write-Host "Thumbprint does NOT match the expected value!"

}

[Step 4]: Using the Authenticated Session to Call the API

After successful authentication, you can use the authenticated session to call your API. The specifics of this depend on your API's authentication requirements (e.g., passing an access token in the Authorization header).

# Example: Get an access token

$token = Get-AzAccessToken -ResourceUrl "your_api_resource_url"

# Example: Call the API

$apiUrl = "your_api_endpoint"

$headers = @{

    "Authorization" = "Bearer $($token.Token)"

}

try {

    $response = Invoke-RestMethod -Uri $apiUrl -Method Get -Headers $headers

    Write-Host "API Response: $($response | ConvertTo-Json)"

} catch {

    Write-Host "Error calling API: $($_.Exception.Message)"

}

Final Answer

Yes, it is possible to use a wildcard certificate for authenticating to an API-driven inbound provisioning application via a service principal in a PowerShell script. You can upload the wildcard certificate to the service principal, authenticate using the certificate in your PowerShell script, and optionally verify the thumbprint for added security.

Highlights

• Wildcard Certificate Scope: Remember that wildcard certificates only cover first-level subdomains. Ensure your API endpoint falls within the scope of the wildcard certificate.
• Certificate Security: Protect your certificate file (especially the .pfx file) and its password. Store them securely and avoid hardcoding them directly in your script. Consider using Azure Key Vault for secure storage and retrieval.
• Error Handling: Implement robust error handling in your PowerShell script to catch potential authentication or API call failures.
• Azure AD Permissions: Ensure the service principal has the necessary permissions to access the API. This is configured in Azure AD.
• Certificate Rotation: Plan for certificate rotation. Certificates expire, so you'll need a process to renew and update the certificate on the service principal and in your PowerShell scripts.

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