How can I implement certificate-based proxy authentication in an iOS VPN app

1. Configure the VPN Server

- Set up the VPN server to use certificate-based authentication for the proxy[1][2][3]
- Ensure the server can identify the user's group based on fields in the client certificate[5]

2. Create a Trusted Certificate Profile in Intune

- Import the VPN server's root certificate issued by the CA into an Intune profile[4]
- This trusted certificate profile instructs the iOS device to automatically trust the CA that the VPN server presents[4]

3. Create a SCEP or PKCS Certificate Profile in Intune

- Configure the SCEP or PKCS certificate profile to provide client credentials to the VPN server[4]
- This allows the device to silently authenticate without prompting for a username and password[4]

4. Create a Per-App VPN Profile in Intune

- Include the SCEP or PKCS certificate with client credentials in the VPN profile[4]
- Configure the VPN connection information and enable the per-app VPN flag[4]
- Set the authentication method to Certificates and select the authentication certificate[4]
- Disable split tunneling to force all traffic through the VPN tunnel[4]

By following these steps to configure certificate-based authentication on the VPN server and create the necessary profiles in Intune, you can implement secure proxy authentication in an iOS VPN app without prompting the user for credentials. The trusted certificate and client certificate allow the device to automatically authenticate with the VPN server.