Technologies for determining a confidence of user authentication include authenticating a user of a computing device based on a set of authentication factors and a fusion function that fuses the set of authentication factors to generate an authentication result. A false accept rate and a false reject rate of the authentication result is determined, and an authentication confidence for the authentication result is determined. The authentication of the user is performed passively, without interruption or interruption of the user. If the authentication confidence is below a threshold value, an active authentication procedure may be performed.