A method for synchronizing an identity of a user between a network observer and a third party includes: reading, by the network observer, a connection request sent from the user to the third party, the connection request including a host field having a host part corresponding to the third party and a sub-host part corresponding to identification information of the user; and associating, by the network observer in a database, the identification information of the user derived from the sub-host part with the identity of the user and an identity of the third party.