Provided is dynamic and flexible authentication based on an interaction over a communications link between a user device and a financial entity. A set of interactions enabled at the user device are categorized into different levels, each level comprises a different authentication policy. At about the same time as an interaction is initiated at the device, an authentication policy assigned to the interaction is accessed and a security challenge is activated at the device. Based upon a successful response to the security challenge, an enablement of the communications link is continued. Based upon an unsuccessful response to the security challenge, the communications link is disabled.