Have you tried to add an Accept header to your request? I ran into the same issue with the Magento API, tested it and found that the PHP OAuth client does not send an accept header by default. So try the following:
$oauthClient->fetch($resourceUrl, array(), 'GET', array('Content-Type' => 'application/xml', 'Accept' => 'application/xml'));
or
$oauthClient->fetch($resourceUrl, array(), 'GET', array('Content-Type' => 'application/xml', 'Accept' => '*/*'));
You can view additional information about the exception using the following when configuring the client:
$oauthClient->enableDebug();
... and then look at debugging with:
$oauthClient->debugInfo
or
$oauthClient->getLastResponse
Other methods are described here:
http://www.php.net/manual/en/class.oauth.php
Sam crithley
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