使用Guzzle php创建oauth1签名

I want to use the Magento 1.x REST API to obtain all the products from the webshop. It uses OAUTH1 but I have some trouble getting it to work using PHP and Guzzle. I have the following information:

$consumerKey = '..';
$consumerSecret = '..';
$token = '..';
$tokenSecret = '..';

Using Postman I can already obtain all the products so I know for sure that the values are correct. My question now is how do I create the signature? I have the following code but it seems to be wrong:

private function buildSignature()
{
    $nonce = uniqid(mt_rand(1, 1000));
    $timestamp = time();
    $consumerKey = 'xx';
    $consumerSecret = 'xx';
    $token = 'xx';
    $tokenSecret = 'xx';

    $base = 'GET&'. rawurlencode('https://www.magentoshop.com/api/rest/products') .'&'.
        rawurlencode('oauth_consumer_key='. $consumerKey) .'&'.
        rawurlencode('oauth_nonce='. $nonce) .'&'.
        rawurlencode('oauth_signature_method=HMAC-SHA1') .'&'.
        rawurlencode('oauth_timestamp='. $timestamp) .'&'.
        rawurlencode('oauth_token='. $token) .'&'.
        rawurlencode('oauth_version=1.0')
    ;
    $key = rawurlencode($consumerSecret) .'&'. rawurlencode($tokenSecret);

    return base64_encode(hash_hmac('sha1', $base, $key, true));
}

The response I get is always: "{"messages":{"error":[{"code":401,"message":"oauth_problem=signature_invalid"}]}}"

What am I doing wrong?

maybe you can review links https://magento.stackexchange.com/questions/147319/error-oauth-problem-signature-invalid-for-post http://developer.pearson.com/creating-and-using-oauth-10a-signature