Authentification Guide — Two authenticators

Configuring the Time-Based One-Time Password (TOTP) Tool for Two-Factor Authentication Using Google Authenticator - NetIQ® CloudAccess and MobileAccess Installation and Configuration Guide

Types of two-factor authentication, pros and cons: SMS, authenticator apps, YubiKey

Client to Authenticator Protocol (CTAP)

Two-factor authentication explained: How to choose the right level of security for every account

Two-factor authentication for your URIports account

Client to Authenticator Protocol (CTAP)

Two Factor Authentication (2FA) - EnterpriseDT

Duo Two Factor Authentication

Two-factor authentication explained: How to choose the right level of security for every account

A Guide to Common Types of Two-Factor Authentication on the Web

How to set up the Two-Step Authorization (Google Authenticator). – Gaijin Support

The Definitive Guide to 2 Factor Authentication - by Arsen

Web Authentication: An API for accessing Public Key Credentials - Level 2

WebAuthn Developer Guide