Passwords alone are not enough. Learn how to implement Two-Factor Authentication in .NET using TOTP, QR codes, and the Otp.NET library, with a secure setup flow and encrypted secrets at rest.

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Milan Jovanović

A practical guide to implementing TOTP-based Two-Factor Authentication in ASP.NET Core. Covers how TOTP works, generating cryptographically secure secret keys with Otp.NET, creating QR codes using QRCoder, the correct two-step setup flow (pending → confirmed), issuing limited-scope tokens during login, validating codes with replay attack prevention via time-step tracking, rate limiting the validation endpoint, encrypting TOTP secrets at rest using AES with a key vault, and generating hashed one-time recovery codes.

How to Implement Two-Factor Authentication in ASP.NET Core