Nowadays, people own and carry an increasing number of mobile devices, such as smartphones and smartwatches. Since these devices store and provide access to sensitive information, authentication is required to prevent unauthorized access. Widely used mechanisms like PIN and password, however, don't scale well with the growing number of devices and interactions. We present the preliminary design of Cormorant, an extensible, risk-aware, multi-modal, crossdevice authentication framework that enables transparent continuous authentication using different biometrics across multiple trusted devices.