title: Access token is empty with GuzzleHttp
body: <p>When I try to make a connection to Microsoft Graph with the following code:</p>
  
  <pre><code>$headers = [
      'Authorization: Bearer ' . $this-&gt;getAccessToken(),
      'Content-Type: application/json;odata.metadata=minimal;odata.streaming=true;IEEE754Compatible=false;charset=utf-8',
      'Preference-Applied: odata.track-changes'
  ];
  $response = $this-&gt;guzzle-&gt;request('GET', 'https://graph.microsoft.com/v1.0/me/calendarview/delta?startdatetime=2017-12-12T00:00:00Z&amp;enddatetime=2020-12-13T00:00:00Z'. ['headers' =&gt; $headers], ['debug' =&gt; true]);
  </code></pre>
  
  <p>Which gives me the error:
  <code>Access token is empty</code></p>
  
  <p>And the debug gives me this:</p>
  
  <blockquote>
    <ul>
    <li>About to connect() to graph.microsoft.com port 443 (#0)</li>
    <li>Trying 40.126.9.112...</li>
    <li>Connected to graph.microsoft.com (40.126.9.112) port 443 (#0)</li>
    <li>Initializing NSS with certpath: sql:/etc/pki/nssdb</li>
    <li>CAfile: /etc/pki/tls/certs/ca-bundle.crt   CApath: none</li>
    <li>SSL connection using TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384</li>
    <li>Server certificate:</li>
    <li>subject: CN=graph.microsoft.com</li>
    <li>start date: Jan 27 19:09:45 2019 GMT</li>
    <li>expire date: Jan 27 19:09:45 2021 GMT</li>
    <li>common name: graph.microsoft.com</li>
    <li>issuer: CN=Microsoft IT TLS CA 2,OU=Microsoft IT,O=Microsoft Corporation,L=Redmond,ST=Washington,C=US
    
    <blockquote>
      <p>GET /v1.0/me/calendarview/delta?startdatetime=2017-12-12T00:00:00Z&amp;enddatetime=2020-12-13T00:00:00ZArray
      HTTP/1.1 User-Agent: GuzzleHttp/6.3.3 curl/7.29.0 PHP/5.6.40 Host:
      graph.microsoft.com</p>
    </blockquote></li>
    </ul>
    
    <p>&lt; HTTP/1.1 401 Unauthorized &lt; Content-Type: application/json;
    charset=utf-8 &lt; request-id: c82bfd7f-921f-40b7-a973-38b6630cb2c2 &lt;
    client-request-id: c82bfd7f-921f-40b7-a973-38b6630cb2c2 &lt;
    x-ms-ags-diagnostic: {"ServerInfo":{"DataCenter":"West
    Europe","Slice":"SliceC","Ring":"5","ScaleUnit":"002","RoleInstance":"AGSFE_IN_45","ADSiteName":"WEU"}}
    &lt; WWW-Authenticate: Bearer realm="",
    authorization_uri="https://login.microsoftonline.com/common/oauth2/authorize",
    client_id="00000003-0000-0000-c000-000000000000" &lt;
    Strict-Transport-Security: max-age=31536000 &lt; Date: Tue, 09 Apr 2019
    08:08:39 GMT &lt; Content-Length: 234</p>
  </blockquote>
  
  <p>Somehow it does work in Postman when I give the same details however like you can see, the code after <code>Bearer</code> is empty. I did check <code>$this-&gt;getAccessToken()</code> and it definitely contains the token.</p>
  
  <p>What am I doing wrong here?</p>