Use TLS/SSL certificates in your application code

In your application code, you can access the public or private certificates that you add to Azure App Service. Your app code might act as a client and access an external service that requires certificate authentication. It might also need to perform cryptographic tasks. This article shows how to use public or private certificates in your application code.

This approach to using certificates in your code makes use of the Transport Layer Security (TLS) functionality in App Service, which requires your app to be in the Basic tier or higher. If your app is in the Free or Shared tier, you can include the certificate file in your app repository.

When you let App Service manage your TLS/Secure Sockets Layer (SSL) certificates, you can maintain the certificates and your application code separately and safeguard your sensitive data.

Prerequisites

To follow this article, see:

• Create an App Service app
• Add a certificate to your app

Find the thumbprint

1. In the Azure portal, on the left pane, select App Services > <app-name>.

2. On the left pane of your app, select Certificates. Then select Bring your own certificates (.pfx) or Public key certificates (.cer).

3. Find the certificate that you want to use and copy the thumbprint.

Make the certificate accessible

To access a certificate in your app code, add its thumbprint to the WEBSITE_LOAD_CERTIFICATES app setting. Run the following command in Azure Cloud Shell:

az webapp config appsettings set --name <app-name> --resource-group <resource-group-name> --settings WEBSITE_LOAD_CERTIFICATES=<comma-separated-certificate-thumbprints>

To make all your certificates accessible, set the value to *.

When WEBSITE_LOAD_CERTIFICATES is set to *, all previously added certificates are accessible to application code. If you add a certificate to your app later, restart the app to make the new certificate accessible to your app. For more information, see Update or renew a certificate.

Load certificates in Windows apps

The WEBSITE_LOAD_CERTIFICATES app setting makes the specified certificates accessible to your Windows hosted app in the Windows certificate store, in Current User\My.

In C# code, you access the certificate by using the certificate thumbprint. The following code loads a certificate with the thumbprint E661583E8FABEF4C0BEF694CBC41C28FB81CD870.

using System;
using System.Linq;
using System.Security.Cryptography.X509Certificates;

string certThumbprint = "E661583E8FABEF4C0BEF694CBC41C28FB81CD870";
bool validOnly = false;

using (X509Store certStore = new X509Store(StoreName.My, StoreLocation.CurrentUser))
{
  certStore.Open(OpenFlags.ReadOnly);

  X509Certificate2Collection certCollection = certStore.Certificates.Find(
                              X509FindType.FindByThumbprint,
                              // Replace below with your certificate's thumbprint
                              certThumbprint,
                              validOnly);
  // Get the first cert with the thumbprint
  X509Certificate2 cert = certCollection.OfType<X509Certificate2>().FirstOrDefault();

  if (cert is null)
      throw new Exception($"Certificate with thumbprint {certThumbprint} was not found");

  // Use certificate
  Console.WriteLine(cert.FriendlyName);
  
  // Consider to call Dispose() on the certificate after it's being used, available in .NET 4.6 and later
}

In Java code, you access the certificate from the Windows-MY store by using the Subject Common Name field. For more information, see Public key certificate. The following code shows how to load a private key certificate:

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.RequestMapping;
import java.security.KeyStore;
import java.security.cert.Certificate;
import java.security.PrivateKey;

...
KeyStore ks = KeyStore.getInstance("Windows-MY");
ks.load(null, null); 
Certificate cert = ks.getCertificate("<subject-cn>");
PrivateKey privKey = (PrivateKey) ks.getKey("<subject-cn>", ("<password>").toCharArray());

// Use the certificate and key
...

For languages that don't support or offer insufficient support for the Windows certificate store, see Load a certificate from a file.

Load a certificate from a file

If you need to load a certificate file that you upload manually, it's better to upload the certificate by using File Transfer Protocol Secure (FTPS) instead of Git, for example. Keep sensitive data like a private certificate out of source control.

ASP.NET and ASP.NET Core on Windows must access the certificate store even if you load a certificate from a file. To load a certificate file in a Windows .NET app, load the current user profile with the following command in Cloud Shell:

az webapp config appsettings set --name <app-name> --resource-group <resource-group-name> --settings WEBSITE_LOAD_USER_PROFILE=1

This approach to using certificates in your code makes use of the TLS functionality in App Service, which requires your app to be in the Basic tier or higher.

The following C# example loads a public certificate from a relative path in your app:

using System;
using System.IO;
using System.Security.Cryptography.X509Certificates;

...
var bytes = File.ReadAllBytes("~/<relative-path-to-cert-file>");
var cert = new X509Certificate2(bytes);

// Use the loaded certificate

To see how to load a TLS/SSL certificate from a file in Node.js, PHP, Python, or Java, see the documentation for the respective language or web platform.

Load certificates in Linux/Windows containers

The WEBSITE_LOAD_CERTIFICATES app setting makes the specified certificates accessible to your Windows or Linux custom containers (including built-in Linux containers) as files. The files are found under the following directories:

The certificate file names are the certificate thumbprints.

In addition, Windows Server Core and Windows Nano Server containers load the certificates into the certificate store automatically, in LocalMachine\My. To load the certificates, follow the same pattern as shown in Load certificates in Windows apps. For Windows Nano-based containers, use the file paths as shown in Load a certificate from a file.

using System;
using System.IO;
using System.Security.Cryptography.X509Certificates;

...
var bytes = File.ReadAllBytes("/var/ssl/certs/<thumbprint>.der");
var cert = new X509Certificate2(bytes);

// Use the loaded certificate

using System;
using System.IO;
using System.Security.Cryptography.X509Certificates;
...
var bytes = File.ReadAllBytes("/var/ssl/private/<thumbprint>.p12");
var cert = new X509Certificate2(bytes);

// Use the loaded certificate

using System;
using System.Linq;
using System.Security.Cryptography.X509Certificates;

string certThumbprint = "E661583E8FABEF4C0BEF694CBC41C28FB81CD870";
bool validOnly = false;

using (X509Store certStore = new X509Store(StoreName.My, StoreLocation.LocalMachine))
{
  certStore.Open(OpenFlags.ReadOnly);

  X509Certificate2Collection certCollection = certStore.Certificates.Find(
                              X509FindType.FindByThumbprint,
                              // Replace below with your certificate's thumbprint
                              certThumbprint,
                              validOnly);
  // Get the first cert with the thumbprint
  X509Certificate2 cert = certCollection.OfType<X509Certificate2>().FirstOrDefault();

  if (cert is null)
      throw new Exception($"Certificate with thumbprint {certThumbprint} was not found");

  // Use certificate
  Console.WriteLine(cert.FriendlyName);
  
  // Consider to call Dispose() on the certificate after it's being used, available in .NET 4.6 and later
}

using System.Security.Cryptography.X509Certificates;

string Thumbprint = "C0CF730E216F5D690D1834446554DF5DC577A78B";

using X509Store store = new X509Store(StoreName.My, StoreLocation.LocalMachine);
{
    store.Open(OpenFlags.ReadOnly);
    
    // Get the first cert with the thumbprint
    var certificate = store.Certificates.OfType<X509Certificate2>()
        .First(c => c.Thumbprint == Thumbprint) ?? throw new Exception($"Certificate with thumbprint {Thumbprint} was not found");

    // Use certificate
    ViewData["certificateDetails"] = certificate.IssuerName.Name.ToString();
}

To see how to load a TLS/SSL certificate from a file in Node.js, PHP, Python, or Java, see the documentation for the respective language or web platform.

Update or renew a certificate

When you renew a certificate and add it to your app, it gets a new thumbprint, which also must be made accessible. How it works depends on your certificate type.

If you manually upload the public or private certificate:

• If you list thumbprints explicitly in WEBSITE_LOAD_CERTIFICATES, add the new thumbprint to the app setting.
• If WEBSITE_LOAD_CERTIFICATES is set to *, restart the app to make the new certificate accessible.

If you renew a certificate in Azure Key Vault, such as with an App Service certificate, the daily sync from Key Vault makes the necessary update automatically when your app synchronizes with the renewed certificate.

• If WEBSITE_LOAD_CERTIFICATES contains the old thumbprint of your renewed certificate, the daily sync updates the old thumbprint to the new thumbprint automatically.
• If WEBSITE_LOAD_CERTIFICATES is set to *, the daily sync makes the new certificate accessible automatically.

Related content

• Secure a custom DNS name with a TLS/SSL binding in Azure App Service
• Enforce HTTPS
• Enforce TLS 1.1/1.2
• FAQ: App Service certificates
• Environment variables and app settings reference