Cloud-connected mobile applications are becoming a popular solution for ubiquitous access to online services, such as cloud data storage platforms. The adoption of such applications has brought security and privacy implications that are making individuals hesitant to migrate sensitive data to the Cloud; thus, new secure authentication protocols are needed. In this paper, we propose a continuous authentication approach integrating physical (face) and behavioral (touch and hand movements) biometrics to control user access to Cloud-based mobile services, going beyond one-off login. Experimental results show the security-usability tradeoff achieved by our approach.