1. A non-transitory computer-readable medium embodying an identity management program executable in a computing device, comprising: code that stores, in a memory, a preconfigured sequence of behavioral events specified by an authenticated user in association with a user identity; code that, in response to receiving an assertion of the user identity from a client and receiving behavior verification data created by a server associated with a first network site, performs a comparison between a plurality of behavioral events and the preconfigured sequence of behavioral events associated with the user identity, the behavior verification data recording the plurality of behavioral events expressed by the client relative to a resource of the first network site, the plurality of behavioral events corresponding to at least one of: a client-side behavior relative to a rendered resource obtained from the first network site, a particular search query being executed in the first network site, a particular item being purchased in the first network site, or a particular resource being accessed; code that generates an identity confidence level as to whether the user identity belongs to a user at the client based at least in part on the comparison; and code that authenticates the user at the client to access a secured resource of a second network site in response to determining that the identity confidence level meets a threshold.