Abstract: A system and method for securely authenticating a user provides the user the convenience of performing a single action to authenticate the user to an online business without any need for the user to enter, much less remember, any credentials specific to logging into the online business. An actionable item is provided to the user via a message sent to a messaging address that the user has provided when signing up with a backend system incorporating the disclosed authentication system. The actionable item, which incorporates authentication-related information for the user, is so formulated that a single action performed on the actionable item causes an authentication request to be sent to the backend system. The backend system, upon receiving the request, authenticates the user using the authentication-related information retrieved from the authentication request. Optionally, the user will be presented a destination page personally selected during the sign-up following a successful authentication.