* @param user The Azure AD user whose tokens need to be refreshed.
     * @return The new authentication result, or null if silent refresh failed.
     */
    public IAuthenticationResult refreshTokenSilently(final AzureAdCredential.AzureAdUser user) {
        final String authority = getAuthority() + getTenant() + "/";
        try {
            final ConfidentialClientApplication app = ConfidentialClientApplication