OmniAuth provides a standardized interface for authenticating with various external providers. Once the user authenticates with the provider, it’s up to us developers to handle the callback and implement actual login and registration into the app. There is a wiki page laying out various scenarios that need to be handled if you want to support multiple providers, showing that it’s by no means a trivial task.| Janko Marohnić
Multi-factor authentication or MFA (generalized two-factor authentication or 2FA) is a method of authentication where the user is required to provide two or more pieces of evidence (“factors”) in order to be granted access. Typically the user would first prove knowledge of something only they know (e.g. their password), and then prove posession of something only they own (e.g. another device). This provides an extra layer of security for the user’s account.| Janko Marohnić