1. A device comprising: at least one processor circuit configured to: identify a first behavioral pattern of a user over a first period of time based at least in part on a first plurality of data items generated by at least one sensor device over the first period of time, wherein the first plurality of data items relate to physical behaviors of the user that are external to the device, and a user signature is generated based at least in part on the first behavioral pattern of the user; receive a request for authentication of the user, the request specifying an authentication level, wherein the authentication level is associated with a behavior deviation level; identify a second behavioral pattern over a second period of time based at least in part on a second plurality of data items generated by the at least one sensor device over the second period of time; determine a degree of deviation of the second behavioral pattern with respect to the user signature; determine whether the degree of deviation satisfies the behavior deviation level associated with the authentication level, wherein different behavior deviation levels are satisfied by different degrees of deviation between the second behavioral pattern and the user signature, the behavior deviation level decreases as the authentication level with which the behavior deviation level is associated increases, and the behavior deviation level increases as the authentication level with which the behavior deviation level is associated decreases; and provide an authentication success indication when the degree of deviation satisfies the behavior deviation level, otherwise providing an authentication failure indication.