default CasRadiusResponse authenticate(final String username, final String password) throws Exception {
        return authenticate(username, password, Optional.empty());
    }
Method to authenticate a set of credentials.

@param username Non-null username to authenticate.
@param password Password to authenticate.
@return {@link CasRadiusResponse} on success, null otherwise.
@throws Exception On indeterminate case where authentication was prevented by a system (e.g. IO) error.
support/cas-server-support-radius-core/src/main/java/org/apereo/cas/adaptors/radius/RadiusServer.java