403 when trying to list web spaces via Azure websites management REST API

I'm just in the process of experimenting with the Azure rest api's in preparation for some work I'm heading into...

Within node.js I'm trying to obtain a list of webspaces hosted by my subscription using the following code...

var websiteOptions = {
    hostname: 'management.core.windows.net',
    path: '/<<Subscription-ID>>/services/webspaces',
    method: 'GET',
    pfx: new Buffer(managementCert, 'base64'),
    strictSSL: true,
    headers: {
        'x-ms-version': '2013-06-01'
    }
};

websiteOptions.agent = new https.Agent(websiteOptions);

var request = https.request(websiteOptions,function(res){
    console.log('Status Code:', res.statusCode);
    console.log('Headers:', res.headers);

When executed it returns back with..

<Error xmlns="http://schemas.microsoft.com/windowsazure"
   xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
   <Code>AuthenticationFailed</Code>
   <Message>The server failed to authenticate the request. Verify that the certificate is valid and is associated with this subscription.
   </Message>
</Error>

The strange thing is that if I replace ..

/<<subscription-ID>>/services/webspaces

with...

/<<subscription-ID>>/services/hostedservices

That specific call works like a charm, returning a list of hosted services - so this leads me to believe that I'm encoding/attaching my management certificate correctly.

I have tried various api versions in the headers without much luck, I have also read various sections of http://msdn.microsoft.com/en-us/library/windowsazure/dn166981.aspx without much luck.

So why are my credentials working in one section of the API and not the websties section

What am I missing, I'm sure it's something really simple :|