Tutorial: Configure External PKI with Easy-RSA⁠

Overview⁠

The Access Server external public key infrastructure (PKI) feature integrates Access Server with third-party tools for X.509 PKI management instead of using the built-in certificate management capabilities.

When configured for external PKI usage, Access Server doesn't manage client certificates directly; instead, the customer's third-party PKI software generates and distributes client certificate/key pairs to client machines and a server certificate/key pair to the OpenVPN server.

This tutorial shows you how to set up an external PKI using Easy-RSA.

At a high level, these are the steps for your configuration:

Modify as.conf to set Access Server in external PKI mode.
Initiate Easy-RSA.
Generate the CA key and certificate via Easy-RSA commands.
Generate the server key and certificate via Easy-RSA commands.
Generate the client key, certificate, and P12 file via Easy-RSA and OpenSSL commands.
Create the TLS_auth key.
Generate Diffie-Hellman parameters.
Import the necessary certificate and key files to Access Server.
Provide certificate/key pairs in a P12/PFX file to the VPN client.
Generate and download a server-locked profile for the client.

Prerequisites⁠

An installed Access Server.
A machine with Easy-RSA and OpenSSL installed. This could be the same Linux where Access Server is installed or an external machine.
Console access and the ability to get root access.
An OpenVPN client that supports the macOS Keychain and Windows certificate store.

Ensure you have Easy-RSA installed:

For Ubuntu/Debian:

sudo apt update
sudo apt install easy-rsa

For RHEL:

sudo yum install epel-release
sudo yum install easy-rsa

Connect to the Access Server console and get root privileges.
Edit as.conf for external PKI usage:
```
nano /usr/local/openvpn_as/etc/as.conf
```

Comment out certs_db:

# certificates database
# certs_db=sqlite:///~/db/certs.db

Save and exit the file — Ctrl-X, Y, then Enter.
- Access Server no longer uses the certificate database. Instead, an external system must handle this.

Run the following commands to initiate Easy-RSA:

cp -r /usr/share/easy-rsa/ /etc/easy-rsa/
cd /etc/easy-rsa/
./easyrsa init-pki

Run the command below to generate the CA certificate and key:
```
./easyrsa build-ca
```
Enter a New CA Key Passphrase at the prompt.
Tip
This is used to sign the remaining certificates.
- You now have two files:
  1. CA key (/etc/easy-rsa/pki/private/ca.key)
  2. CA certificate (/etc/easy-rsa/pki/ca.crt)

Open the x509-types/server file to edit (we use nano):
```
nano x509-types/server
```

Remove the contents of this file and add these lines:

basicConstraints = critical, CA:FALSE
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always

Save and exit the file — ctrl + x, y, then enter.

Open the x509-types/client file to edit (we use nano):
```
nano x509-types/client
```

Remove the contents of this file and add these lines:

basicConstraints = critical, CA:FALSE
keyUsage = critical, digitalSignature
extendedKeyUsage = clientAuth
nsCertType = client
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always

Save and exit the file — ctrl + x, y, then enter.

Run the below command to generate the server CSR:
```
./easyrsa gen-req server nopass
```
- You'll be asked to enter the CN of the Server Certificate (e.g., OpenVPN Server).
Run the below command to generate the server certificate with the custom OpenSSL file created in Step 4:
```
./easyrsa --req-cn="OpenVPN Server" sign-req server server
```
- You now have two files:
  1. Server key (/etc/easy-rsa/pki/private/server.key)
  2. Server certificate (/etc/easy-rsa/pki/issued/server.crt)

Run the below command to generate the client CSR:
```
./easyrsa gen-req etest nopass
```
- You'll be asked to enter the CN of the Client Certificate (e.g., etest).
Run the below command to generate the client certificate with the custom OpenSSL file created in Step 5:
```
./easyrsa --req-cn="etest" sign-req client etest
```

Generate a P12 file with the client certificate and key:

openssl pkcs12 -export -inkey /etc/easy-rsa/pki/private/etest.key -in /etc/easy-rsa/pki/issued/etest.crt -out /etc/easy-rsa/pki/etest.p12 -name "etest"

If you're using Easy-RSA version 3.2.1, you need to run the following command:

openssl pkcs12 -export -inkey /etc/easy-rsa/3.2.1/pki/private/etest.key -in /etc/easy-rsa/3.2.1/pki/issued/etest.crt -out /etc/easy-rsa/3.2.1/pki/etest.p12 -name "etest"

You'll be prompted to enter a password for the P12 file. Type it twice.
- You now have three files:
  1. Client key (/etc/easy-rsa/pki/private/etest.key)
  2. Client certificate (/etc/easy-rsa/pki/issued/etest.crt)
  3. P12 file (/etc/easy-rsa/pki/etest.p12)

Connect to the Access Server console and get root privileges.
Create a directory:
```
cd .. && mkdir epki && cd epki
```

Place the CA certificate, server certificate, and key generated from the Easy-RSA commands in the new epki directory:

cp /etc/easy-rsa/pki/ca.crt ./
cp /etc/easy-rsa/pki/issued/server.crt ./
cp /etc/easy-rsa/pki/private/server.key ./

If you're using Easy-RSA version 3.2.1, run the following commands:

cp /etc/easy-rsa/3.2.1/pki/ca.crt ./
cp /etc/easy-rsa/3.2.1/pki/issued/server.crt ./
cp /etc/easy-rsa/3.2.1/pki/private/server.key ./

Create a tls_auth key for the OpenVPN server:

/usr/local/openvpn_as/scripts/certool --tls_auth

Generate Diffie Hellman parameters for the OpenVPN server:
```
openssl dhparam -out dh.pem 2048
```
For Access Server 2.7 and newer, you must also generate your auth token and add the generated file:
```
/usr/local/openvpn_as/scripts/certool --auth_token
```
Configure X509 explicit/extended key usage based on RFC3280 TLS rules:
```
sacli --key "external_pki.remote_cert_usage" --value eku ConfigPut
```
Configure the use of the X509 “role” attribute for the declaration of auto-login permission:
```
sacli --key "external_pki.autologin_x509_spec" --value "role,,AUTOLOGIN" ConfigPut
```
Generate the tls-crypt-v2 key (for Access Server 2.9.0 and higher only):
```
/usr/local/openvpn_as/scripts/certool --tls_crypt2_server
```

Load the newly generated files into the Access Server config database:

sacli --key "external_pki.ta_key" --value_file ta.key ConfigPut
sacli --key "external_pki.ca_crt" --value_file ca.crt ConfigPut
sacli --key "external_pki.server_crt" --value_file server.crt ConfigPut
sacli --key "external_pki.server_key" --value_file server.key ConfigPut
sacli --key "external_pki.dh_pem" --value_file dh.pem ConfigPut
sacli --key "external_pki.auth_token_key" --value_file auth_token.key ConfigPut
sacli --key "external_pki.tls_cryptv2_server" --value_file tls_crypt2.key ConfigPut

Start Access Server:
```
systemctl restart openvpnas
```

To test our example, we generate a test client, etest.

Sign in to the Admin Web UI.
Select Users.
Select Add New User.
- The New User modal displays.
Enter the new username, "etest," and assign to a group, then select Save.
- The single user page for "etest" is displayed.
Select Restart.
Generate a server-locked profile. The profile will be stored in etest.ovpn:
```
/usr/local/openvpn_as/scripts/sacli GetGeneric >etest.ovpn
```
Copy these two files to the client machine:
- Client P12 file (etest.p12)
- Client profile (etest.ovpn)
Install the profile and P12 file in OpenVPN Connect v3:
1. Launch OpenVPN Connect v3.
2. Import the connection profile, etest.ovpn.
3. Select Certificate & Tokens.
4. Under PKCS#12, select the Add icon.
5. Select your client P12 file etest.p12.
6. Enter the password for this file that you configured in step 7 and click OK.
7. Select My Profiles and edit the profile.
8. Under Certificates, use the Select button to add the external certificate to the profile.
9. Select the P12 file.
10. Select Save Changes.
11. Select Connect to start the profile connection.

With the release of Access Server 2.14.2, we've made configuring client connection profiles for ePKI easier. Previously, creating these profiles required using the command line, as noted in the tutorial. However, in version 2.14.2 and later, you can now create and manage ePKI client connection profiles directly from Access Server's Client Web UI.

There are two types of ePKI profiles available:

Generic ePKI profile:
- This profile requires the user to authenticate with a password when connecting.
- Ideal for environments where a password-based security layer is needed in addition to certificate-based authentication.
Auto-login ePKI profile;
- This profile automatically uses the certificate for authentication without requiring a password.
- Suitable for unattended devices or systems where automatic, certificate-based login is needed.

In addition, the Import Profile from URL functionality in OpenVPN Connect allows users to import these connection profiles directly, making the configuration process faster and more seamless.

This update simplifies the ePKI setup, providing more flexibility and reducing the reliance on the command line.

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Tutorial: Configure External PKI with Easy-RSA⁠

Overview⁠

Prerequisites⁠

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