1. A mobile device comprising: a contextual sensor; and a processor configured to: implement a background authentication process in a continuous manner based upon a soft biometric input from a biometric sensor and a contextual input from the contextual sensor, wherein the soft biometric input from the biometric sensor includes biometric input received from a user implicitly, wherein the soft biometric sensor is configured to scan one or more physical attributes of the user without alerting the user that the scan is being performed; determine an anomaly event based on the soft biometric input; based upon the anomaly event, request a discrete authentication input comprising an explicit audio authentication input from the user that meets or exceeds a verification level determined based on the anomaly event; authenticating the user using the discrete authentication input; and locking the mobile device responsive to the discrete authentication input failing to authenticate the user.