A computer system receives a service request over a service channel from a user device, initiates a challenge to the user device to provide authentication information based on a set of authenticators, and determines an initial level of authentication. When the initial level of authentication is not sufficient for the service channel or protected resource, the apparatus generates a challenge to the user device with at least one additional authenticator and determines an achieved level of authentication based on the further authentication information. When the achieved level of authentication reaches a target authentication level for the service channel, the apparatus continues processing the service request by the service channel. The computer may transfer the service request to another service channel with the authentication token obtained on the original service channel and further challenges the user device with additional authenticators when a higher level of authentication is necessary.