Cloudflare’s Mutual Auth (TLS Client Auth) creates a secure connection between a client, like an IoT device or a mobile app, and its origin. When a client attempts to establish a connection with its origin server, Cloudflare validates the device’s certificate to check it has authorized access to the endpoint. If the device has a valid client certificate, like having the correct key to enter a building, the device is able to establish a secure connection. If the device’s certificate is missing, expired, or invalid, the connection is revoked and Cloudflare returns a 403 error.