Securing Microsoft Entra Applications: Blocking Client Secrets for Stronger Authentication

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Introduction

Client secrets in Microsoft Entra (formerly Azure AD) are widely used for app authentication but pose significant security risks. Exposed secrets can lead to API breaches, making certificate-based authentication a safer alternative. This article explores how to block client secret creation and enforce stronger security measures.

Learning Objectives

  • Understand the risks of client secrets in Entra applications.
  • Learn how to block client secret creation at the tenant or app level.
  • Implement certificate-based authentication for secure API access.

You Should Know

1. Blocking Client Secrets Across the Entire Tenant

Command (PowerShell):

New-MgPolicyApplicationManagementPolicy -IsEnabled $true -RestrictPublicClientSecretCreation $true

Step-by-Step Guide:

  1. Install the Microsoft Graph PowerShell SDK (Install-Module Microsoft.Graph).
  2. Connect to Microsoft Graph with Connect-MgGraph -Scopes "Policy.ReadWrite.ApplicationConfiguration".
  3. Run the command above to enforce tenant-wide client secret restrictions.

4. Verify enforcement with `Get-MgPolicyApplicationManagementPolicy`.

This policy prevents new client secrets from being created in any Entra application, forcing certificate-based authentication.

2. Restricting Client Secrets for Specific High-Risk Apps

Command (PowerShell):

Update-MgApplication -ApplicationId <AppId> -PasswordCredentials @()

Step-by-Step Guide:

1. Identify high-risk apps using `Get-MgApplication`.

  1. For each app, clear existing secrets with the command above.
  2. Configure certificate authentication via the Entra portal or Graph API.

This granular approach ensures sensitive apps use certificates while allowing secrets for less critical workloads.

3. Enforcing Certificate-Based Authentication

Command (PowerShell):

New-MgApplication -DisplayName "SecureApp" -KeyCredentials @{ 
Type = "AsymmetricX509Cert"; 
Usage = "Verify"; 
Key = [System.Convert]::ToBase64String($cert.RawData) 
}

Step-by-Step Guide:

1. Generate a self-signed or CA-issued certificate.

  1. Use the command to register an app with certificate authentication.

3. Assign API permissions via `Add-MgApplicationPermission`.

Certificates eliminate secret leakage risks and support automated rotation.

4. Monitoring Client Secret Usage

Command (Kusto Query for Azure Sentinel/Microsoft Defender):

SigninLogs 
| where AppDisplayName has "YourApp" 
| where AuthenticationDetails has "clientSecret" 
| project TimeGenerated, UserPrincipalName, IPAddress

Step-by-Step Guide:

  1. Navigate to Microsoft Defender for Cloud or Azure Sentinel.
  2. Run the query to detect apps still using secrets.

3. Set alerts for unauthorized secret-based logins.

5. Automating Secret Expiry and Rotation

Command (Azure CLI):

az ad app credential reset --id <AppId> --append --years 1

Step-by-Step Guide:

  1. Use Azure CLI to enforce yearly secret rotation.

2. Combine with Azure Automation for scheduled resets.

  1. Log rotations in Azure Monitor for audit trails.

What Undercode Say

  • Key Takeaway 1: Client secrets are a weak link in API security—certificates provide a robust alternative.
  • Key Takeaway 2: Proactive policy enforcement reduces breach risks before attackers exploit leaked secrets.

Analysis:

Microsoft Entra’s shift toward certificate-based authentication reflects broader industry trends favoring hardware-backed credentials. While client secrets offer simplicity, their misuse has led to high-profile breaches (e.g., SolarWinds). Enterprises adopting zero-trust frameworks should prioritize this mitigation. Future updates may integrate quantum-resistant algorithms, but today’s certificates already offer a 10x improvement in secret security.

Prediction

By 2026, 80% of enterprises will phase out client secrets for critical apps, driven by compliance mandates (e.g., CISA’s Secure by Design) and AI-powered credential theft. Cloud providers will likely embed secretless authentication by default, rendering manual secret management obsolete.

For further reading, refer to Microsoft’s App Management Policy Guide.

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