A device transmits an instruction for completing a human authentication challenge, to access a server device. The instruction includes information indicating a biometric parameter to be provided by a user, and information indicating a task, to be performed by the user, for varying the biometric parameter. The device receives a request to validate performance of the task. The device obtains a first measurement of the biometric parameter, provided by the user at a first point in time, and obtains a second measurement of the biometric parameter, provided by the user at a second point in time that is later than the first point in time. The device compares the first measurement and the second measurement, and selectively validates the request, based on a result of comparing the first measurement and the second measurement, to selectively grant access to the server device.
