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Your login flow is not complete without 2FA. In this video, I show you how to implement TOTP-based two-factor authentication in .NET from scratch.

We walk through how time-based one-time passwords work, how to generate and share a secret using a QR code, and how to validate codes in your API using a practical .NET implementation. I also cover the production details that matter, like encrypting secrets at rest, handling clock drift, and thinking through recovery flows.

In this video, we cover:

- What 2FA and TOTP are, and why they improve application security
- How authenticator apps like Google Authenticator and Microsoft Authenticator fit into the flow
- Generating a shared secret and encoding it for QR code setup
- Building a QR code endpoint in a .NET 10 API
- Validating one-time passwords with OTP.NET
- Handling verification windows and clock synchronization issues
- Why secret keys must be encrypted at rest
- What a production-ready 2FA flow still needs, like recovery options and proper secret storage

This is a practical walkthrough for .NET developers who want to understand both the implementation and the security tradeoffs behind adding 2FA to a real application.

How to Implement Two-Factor Authentication in ASP.NET Core
https://www.milanjovanovic.tech/blog/how-to-implement-two-factor-authentication-in-aspnetcore

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Chapters

We Are .NET

A practical guide to implementing TOTP-based two-factor authentication in .NET applications. Covers the RFC 6238 standard, generating secret keys with the OTP.NET library, creating QR codes using QRCoder for authenticator apps like Google Authenticator, and validating time-based one-time passwords. Also discusses security hardening requirements such as encrypting secrets at rest, handling clock skew with verification windows, and account recovery considerations.

How to Implement TOTP-Based 2FA in .NET the Right Way