Configure OpenVPN 2.x client for P2S certificate authentication connections - Windows

Article
11/08/2024

If your point-to-site (P2S) VPN gateway is configured to use OpenVPN and certificate authentication, you can connect to your virtual network using the OpenVPN Client. This article walks you through the steps to configure the OpenVPN client 2.4 and higher and connect to your virtual network.

Before you begin

Before beginning client configuration steps, verify that you're on the correct VPN client configuration article. The following table shows the configuration articles available for VPN Gateway point-to-site VPN clients. Steps differ, depending on the authentication type, tunnel type, and the client OS.

Authentication	Tunnel type	Client OS	VPN client
Certificate
	IKEv2, SSTP	Windows	Native VPN client
	IKEv2	macOS	Native VPN client
	IKEv2	Linux	strongSwan
	OpenVPN	Windows	Azure VPN client OpenVPN client version 2.x OpenVPN client version 3.x
	OpenVPN	macOS	OpenVPN client
	OpenVPN	Linux	Azure VPN Client OpenVPN client
Microsoft Entra ID
	OpenVPN	Windows	Azure VPN client

Note

The OpenVPN client is independently managed and not under Microsoft's control. This means Microsoft does not oversee its code, builds, roadmap, or legal aspects. Should customers encounter any bugs or issues with the OpenVPN client, they should directly contact OpenVPN Inc. support. The guidelines in this article are provided 'as is' and have not been validated by OpenVPN Inc. They are intended to assist customers who are already familiar with the client and wish to use it to connect to the Azure VPN Gateway in a Point-to-Site VPN setup.

Prerequisites

This article assumes that you've already performed the following prerequisites:

You created and configured your VPN gateway for point-to-site certificate authentication and the OpenVPN tunnel type. See Configure server settings for P2S VPN Gateway connections - certificate authentication for steps.
You generated and downloaded the VPN client configuration files. See Generate VPN client profile configuration files for steps.
You can either generate client certificates, or acquire the appropriate client certificates necessary for authentication.

Connection requirements

To connect to Azure using the OpenVPN client using certificate authentication, each connecting client computer requires the following items:

The Open VPN Client software must be installed and configured on each client computer.
The client computer must have a client certificate that's installed locally.

Workflow

The workflow for this article is:

Generate and install client certificates if you haven't already done so.
View the VPN client profile configuration files contained in the VPN client profile configuration package that you generated.
Configure the OpenVPN client.
Connect to Azure.

Generate and install client certificates

For certificate authentication, a client certificate must be installed on each client computer. The client certificate you want to use must be exported with the private key, and must contain all certificates in the certification path. Additionally, for some configurations, you'll also need to install root certificate information.

In many cases, you can install the client certificate directly on the client computer by double-clicking. However, for certain OpenVPN client configurations, you might need to extract information from the client certificate in order to complete the configuration.

For information about working with certificates, see Point-to site: Generate certificates.
To view an installed client certificate, open Manage User Certificates. The client certificate is installed in Current User\Personal\Certificates.

Install the client certificate

Each computer needs a client certificate in order to authenticate. If the client certificate isn't already installed on the local computer, you can install it using the following steps:

Locate the client certificate. For more information about client certificates, see Install client certificates.
Install the client certificate. Typically, you can do this by double-clicking the certificate file and providing a password (if required).

View configuration files

The VPN client profile configuration package contains specific folders. The files within the folders contain the settings needed to configure the VPN client profile on the client computer. The files and the settings they contain are specific to the VPN gateway and the type of authentication and tunnel your VPN gateway is configured to use.

Locate and unzip the VPN client profile configuration package you generated. For Certificate authentication and OpenVPN, you should see the OpenVPN folder. If you don't see the folder, verify the following items:

Verify that your VPN gateway is configured to use the OpenVPN tunnel type.
If you're using Microsoft Entra authentication, you might not have an OpenVPN folder. See the Microsoft Entra ID configuration article instead.

Configure the client

Download and install the OpenVPN client (version 2.4 or higher) from the official OpenVPN website.
Locate the VPN client profile configuration package that you generated and downloaded to your computer. Extract the package. Go to the OpenVPN folder and open the vpnconfig.ovpn configuration file using Notepad.
Next, locate the child certificate you created. If you don't have the certificate, use one of the following links for steps to export the certificate. You'll use the certificate information in the next step.
- VPN Gateway instructions
- Virtual WAN instructions
From the child certificate, extract the private key and the base64 thumbprint from the .pfx. There are multiple ways to do this. Using OpenSSL on your computer is one way. The profileinfo.txt file contains the private key and the thumbprint for the CA and the Client certificate. Be sure to use the thumbprint of the client certificate.
```
openssl pkcs12 -in "filename.pfx" -nodes -out "profileinfo.txt"
```
Switch to the vpnconfig.ovpn file you opened in Notepad. Fill in the section between <cert> and </cert>, getting the values for $CLIENT_CERTIFICATE, $INTERMEDIATE_CERTIFICATE, and $ROOT_CERTIFICATE as shown in the following example.
```
   # P2S client certificate
   # please fill this field with a PEM formatted cert
   <cert>
   $CLIENT_CERTIFICATE
   $INTERMEDIATE_CERTIFICATE (optional)
   $ROOT_CERTIFICATE
   </cert>
```
- Open profileinfo.txt from the previous step in Notepad. You can identify each certificate by looking at the subject= line. For example, if your child certificate is called P2SChildCert, your client certificate will be after the subject=CN = P2SChildCert attribute.
- For each certificate in the chain, copy the text (including and between) "-----BEGIN CERTIFICATE-----" and "-----END CERTIFICATE-----".
- Only include an $INTERMEDIATE_CERTIFICATE value if you have an intermediate certificate in your profileinfo.txt file.
Open the profileinfo.txt in Notepad. To get the private key, select the text (including and between) "-----BEGIN PRIVATE KEY-----" and "-----END PRIVATE KEY-----" and copy it.
Go back to the vpnconfig.ovpn file in Notepad and find this section. Paste the private key replacing everything between and <key> and </key>.
```
# P2S client root certificate private key
# please fill this field with a PEM formatted key
<key>
$PRIVATEKEY
</key>
```
If you're using the 2.6 version of the OpenVPN client, add the "disable-dco" option to the profile. This option doesn't seem to be backward compatible with previous versions, so it should only be added to OpenVPN client version 2.6.
Don't change any other fields. Use the filled in configuration in client input to connect to the VPN.
Copy the vpnconfig.ovpn file to C:\Program Files\OpenVPN\config folder.
Right-click the OpenVPN icon in the system tray and click Connect.

Next steps

Follow up with any additional server or connection settings. See Point-to-site configuration steps.