A user, using a user-computing device connected to a computer network, is authenticated to access a computing resource managed by a system on the computer network. The user computing device presents a user interface to prompt the user to input a value for each of a set of user-defined credentials that the user has previously defined for a SAIF server to authenticate the user to access the computer resource, thereby forming a set of input values. Modified values, each generated from and representing a corresponding one of the input values, are transmitted and validated by comparing them with corresponding modified forms of user-defined credential values stored in a memory, thereby determining whether the user is authenticated to access the computing resource on the system.