private static TokenRequestException onUnauthorizedError(AggregatedHttpResponse errorResponse) {
        final StringBuilder messageBuilder = new StringBuilder().append(errorResponse.status());
        final String wwwAuthenticate = errorResponse.headers().get(HttpHeaderNames.WWW_AUTHENTICATE);
        if (wwwAuthenticate != null) {
            messageBuilder.append(": ").append(wwwAuthenticate);
        }
        final HttpData errorResponseContents = errorResponse.content();
        if (!errorResponseContents.isEmpty()) {
            messageBuilder.append(": ").append(errorResponseContents.toStringUtf8());
        }
        return new InvalidClientException(messageBuilder.toString(), null);
    }
Composes {@link InvalidClientException} upon 401 Unauthorized response
as per <a href="https://datatracker.ietf.org/doc/html/rfc6749#section-5.2">[RFC6749], Section 5.2</a> (invalid_client).

@param errorResponse response received from the server

@return an instance of {@link InvalidClientException}
oauth2/src/main/java/com/linecorp/armeria/internal/common/auth/oauth2/AbstractOAuth2ResponseHandler.java