@Override
    public String getId() {
        return getPrincipal().getId();
    }
This is {@link DuoSecurityDirectCredential}.

@author Misagh Moayyed
@since 5.0.0
support/cas-server-support-duo-core-mfa/src/main/java/org/apereo/cas/adaptors/duo/authn/DuoSecurityDirectCredential.java