public Builder fullName(final String fullName) {
            this.fullName = fullName;
            return this;
        }
The unique identifier for this user on the IDP, i.e. the subject. May not be unique within stroom as
we may be using an external IDP but still using the internal IDP for processing user.
If isGroup is true then this is the name of the group.
stroom-core-shared/src/main/java/stroom/security/shared/User.java