A system for authenticating and/or authorizing users of a service includes one communication interface with an access communication channel and another communication interface with a confirmation communication channel. Requests for a user to access a service are received over the access communication channel, and confirmation codes for the user are received over a trusted confirmation channel, such as an SMS text messaging system. Confirmation codes may be received from the user requesting access to the service or by a third party acting as a gatekeeper to the service. The system tests the validity of received confirmation codes, and enables the user to access the service if a valid confirmation code is received.