1. A method for implicitly authenticating a user to access a controlled resource, the method comprising: receiving, from a computing device, a request to access the controlled resource; selecting a user behavior model for the user, wherein the user behavior model is derived from historical contextual data of the user; determining recent contextual data of the user, wherein the recent contextual data are collected from one or more user devices without prompting the user to perform an action associated with authentication, and wherein the recent contextual data comprise a plurality of data streams which provide a basis for determining whether the user owns the computing device; determining a user behavior score which indicates a likelihood that the user owns the computing device, wherein determining the user behavior score involves: observing a recent event that is associated with the user's computing device; calculating a quality measure for the recent event, and a weight associated with a type of the observation; determining that the observed recent event is consistent with the user behavior model; and adjusting the user behavior score based on the quality measure and the weight; and providing the user behavior score to an access controller of the controlled resource, wherein the access controller facilitates access to the controlled resource for the user in response to the user behavior score exceeding a predetermined threshold value.
1. A method for implicitly authenticating a user to access a controlled resource, the method comprising: receiving, from a computing device, a request to access the controlled resource; selecting a user behavior model for the user, wherein the user behavior model is derived from historical contextual data of the user; determining recent contextual data of the user, wherein the recent contextual data are collected from one or more user devices without prompting the user to perform an action associated with authentication, and wherein the recent contextual data comprise a plurality of data streams which provide a basis for determining whether the user owns the computing device; determining a user behavior score which indicates a likelihood that the user owns the computing device, wherein determining the user behavior score involves: observing a recent event that is associated with the user's computing device; calculating a quality measure for the recent event, and a weight associated with a type of the observation; determining that the observed recent event is consistent with the user behavior model; and adjusting the user behavior score based on the quality measure and the weight; and providing the user behavior score to an access controller of the controlled resource, wherein the access controller facilitates access to the controlled resource for the user in response to the user behavior score exceeding a predetermined threshold value. 10. The method of claim 1 , further comprising deriving the user behavior model from a second user behavior model of a group of users sharing similar characteristics.