protected Http buildHttpPostUserPreAuthRequest(final String username) throws Exception {
        val request = buildHttpRequest("/auth/v%s/preauth");
        request.addParam("username", username);
        configureHttpRequest(request);
        return request;
    }
This is {@link BaseDuoSecurityAuthenticationService}.

@author Misagh Moayyed
@since 5.1.0
support/cas-server-support-duo-core/src/main/java/org/apereo/cas/adaptors/duo/authn/BaseDuoSecurityAuthenticationService.java