An approach is provided for authenticating and/or identifying a user through machine-transferrable one-time password codes. A user device sends to an authentication platform a request for a one-time password for authenticating a user at a relying party device. A machine readable form of the one-time password deliverable to the relying party device over an air gap between the user device and the relying party device is determined and transmitted. The relying party device reverts the machine readable form back to the one-time password, and transmits the one-time password to the authentication platform to authenticate the user device.