title: Authentication error using OAuth with exchangelib
body: <p>I am working on a Python based client code to access Microsoft Outlook 365 emails via OAuth2 and get all emails. But when I try to connect with my OAuth credentials, I get an <code>UnauthorizedError</code>.</p>
  <pre class="lang-py prettyprint-override"><code>creds = OAuth2Credentials(
      client_id=CLIENT_ID,
      client_secret=CLIENT_SECRET,
      tenant_id=TENANT_ID,
      identity=Identity(primary_smtp_address='x@y'),
  )
  cfg = Configuration(
      server='outlook.office365.com',
      credentials=creds,
      auth_type=OAUTH2,
  )
  
  #FIXME Following line attempts to create a session with EWS. Currently failing
  account = Account(
      primary_smtp_address='x@y',
      config=cfg,
      autodiscover=False,
      access_type=DELEGATE,
  )
  </code></pre>