The objective of this paper is to introduce a scheme of comprehensive-factor authentication in edge computing, focusing on a case study of time attendance in smart environments. This authentication scheme deploys all possible factors to maximize security while maintaining usability at a specific smart context. The factors used include three classic elements: something you know, something you have, and something you are, plus an additional location factor. The usability issue involves the ability to reduce time used and to minimize the human actions required throughout the authentication process. The results show that all factors should be authenticated at once in background, and a user can successfully complete the authentication process by performing one or two actions simultaneously. Since user role in a smart environment can be more complicated than roles in other smart offices, role classification at an early stage is highly recommended. The case study reveals that the same setting can require varying levels of security and usability for each user.