Twilio has developed a solution that integrates its 2-factor authentication (2FA) service with the FreeRADIUS RADIUS server, which is widely used for authenticating VPN users. This integration allows users to receive push notifications or time-based one-time passwords (TOTPs) for an additional layer of security when accessing the internet via VPNs like OpenVPN and Cisco AnyConnect. The solution works through four different workflows: SoftToken authentication with challenge response, SoftToken authentication without challenge response, OneTouch authentication, and a combination of push notification 2FA with TOTP fallback. This integration is designed to provide flexibility in choosing the best approach for user experience, allowing users to select from various configurations and messaging options.