TOTP-backed Passwordless Auth in C# Using Twilio Verify

C# port of the PHP sample in the parent folder. Implements the same three-step TOTP setup flow against the Twilio Verify API:

1. / — enter a username, which creates a new TOTP factor on a random entity identity
2. /challenge — scan the QR code in an authenticator app and submit the generated code to verify the factor
3. /token — submit subsequent codes to create a challenge and confirm the factor still works

Prerequisites

• .NET 9 SDK
• A Twilio account with a Verify Service. Get the Service SID from https://console.twilio.com/us1/develop/verify/services

Setup

cp .env.example .env
# fill in TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN, TWILIO_VERIFY_SERVICE_SID
dotnet run

Then open http://localhost:5000 (the actual URL is printed at startup).

Structure

• Program.cs — loads .env, initializes the Twilio client, wires up sessions and Razor Pages
• Pages/Index.* — username form and TOTP factor creation
• Pages/Challenge.* — QR code display and factor verification
• Pages/Token.* — ongoing challenge creation and verification
• wwwroot/css/styles.css — styling

The QR code is generated locally with QRCoder and inlined as a base64 PNG data URI.