Google Authenticator - Google Authenticator is a multifactor app for mobile devices.
DotNetOpenAuth - DotNetOpenAuth is a free-to-use compiled library that comes with the real support to your site visitor to login with the help of openIDs via getting control of the ASP.NET control onto the page.
Microsoft Authenticator - One app to quickly and securely verify your identity online, for all of your accounts.
IdentityServer - An open-source, standards-compliant, and flexible OpenID Connect and OAuth 2.x framework for ASP.NET Core
andOTP - andOTP is a two-factor authentication App for Android 4.4+
Okta Workforce Identity - Okta Workforce Identity is utility software for enterprises that provides a new way of work that enable your employees, contractors, and partners to use technology on any device.