title: Does Mule support password grant type for OAuth2
body: <p>I looked at mule-oauth2.xsd and found only client credentials and authorization grant type elements.  However, looking at the oauth2-provider:config it can be configured as supportedGrantTypes="RESOURCE_OWNER_PASSWORD_CREDENTIALS". If it does support resource owner password credentials, how can I configure an oauth2-client to retrieve a token? I am looking at retrieving a token from the OAuth2 provider using the oauth2:client. Here is an example of what I'm referring to, however, I want to achieve this for password.</p>
  
  <pre><code> &lt;http:request-config name="requestConfigWithOAuth"&gt;
      &lt;oauth2:client-credentials-grant-type
              clientId="${client.id}"
              clientSecret="${client.secret}"
              tokenManager-ref="tokenManagerConfig"&gt;
          &lt;oauth2:token-request tokenUrl="${token.url}"/&gt;
      &lt;/oauth2:client-credentials-grant-type&gt;
  &lt;/http:request-config&gt;
  </code></pre>