In this paper, we are concerned by the configuration of authentication mechanisms and how tuning parameters values might affect at the same time the usability and the security of systems. Both usability and security are important properties for interactive systems however, tuning the application (for example to reduce the number of trials) to favor one property (such as security) might decrease another (usability), and vice-versa. In order to investigate the dependencies between usability and security, we propose in this paper a testbed environment for supporting the comparative assessment of authentication mechanisms. The tool presented in this paper allows varying parameters of authentication mechanisms to settle multiple configurations. It integrates a log mechanism for precisely recording the users' interactions. The current implementation features a mobile application that embeds three authentications mechanism, namely: PIN code, Android Pattern Lock and Passface. Nonetheless, the approach can be easily extended to include other authentication mechanisms. The ultimate goal of this testbed is to support user testing of authentication mechanisms and compare the relationship between user's behavior and risk assessment of multiple configurations.