Users with limited use of their hands, such as people suffering from disabilities of the arm, shoulder, and hand (DASH), face challenges when authenticating with computer terminals, specially with publicly accessible terminals such as ATMs. When authentication through a password or PIN is possible, these users have an additional reason to choose a short "easy" combination due to the difficulties involved with entering lengthy convoluted passwords. Access tokens, like smartcards, can assist, however, they require that the user can physically handle such a token and custom reading sensors need to be installed in access terminals. Similar authentication challenges are also present in environments where users need to frequently authenticate and log out or require hands-free authentication, like in hospitals.A new glass wearable device was recently introduced by Google and it was immediately welcomed by groups of users, such as the ones described above, as Google Glass allows them to perform actions, like taking a photo, using only verbal commands. This paper investigates whether glass wearable devices can be used to authenticate users, both to grant access (one-time) and to maintain access (continuous), in similar hands-free fashion. We do so by designing and implementing Gauth, a system that enables users to authenticate with a service simply by issuing a voice command, while facing the computer terminal they are going to use to access the service. To achieve this goal, we create a physical communication channel from the terminal to the device using machine readable visual codes, like QR codes, and utilize the device's network adapter to communicate directly with a service. More importantly, we continuously authenticate the user accessing the terminal, exploiting the fact that a user operating a terminal is most likely facing it most of the time. We periodically issue authentication challenges, which are displayed as a QR code on the terminal, that cause the glass device to re-authenticate the user with an appropriate response. We evaluate our system to determine the technical limits of our approach. We show that even with the relatively low-resolution camera of the current Google Glass prototype, QR codes can be consistently processed correctly (with an average accuracy of 87.8%), and continuous authentication, while strenuous to the battery, is feasible. Finally, we perform a small user study involving students to demonstrate the benefits our approach. We found that authenticating using Gauth takes on average 1.63 seconds, while using username/password credentials takes 3.85 seconds and varies greatly depending on the computer-literacy level of the user.