title: Error: Argument error: username and password are required unless use_unauthenticated is set
body: <p>I'm attempting to use STT service with the iam apikey. </p>
  
  <p>If I set the IAM credentials like the <a href="https://cloud.ibm.com/apidocs/speech-to-text?code=node#authentication" rel="nofollow noreferrer">documentation shows</a> (below) I get the error: username and password are required unless use_unauthenticated is set</p>
  
  <pre><code>let speech_to_text = new SpeechToTextV1({
    iam_apikey: STT_credentials.apikey,
    iam_url: STT_credentials.url
  });
  </code></pre>
  
  <p>If I pass the use_anauthenticated value I get a 401 response:</p>
  
  <pre><code>let speech_to_text = new SpeechToTextV1({
    iam_apikey: STT_credentials.apikey,
    iam_url: STT_credentials.url,
    use_unauthenticated: true
  });
  </code></pre>
  
  <p>response:</p>
  
  <pre><code>Error! Code:401 Type: undefined Message: Unauthorized
  </code></pre>
  
  <p>If I look at the file in the error:</p>
  
  <pre><code>/Users/jward/Desktop/speech_lab_assets/STT/node_mod
  ules/watson-developer-cloud/lib/base_service.js:73:13
  </code></pre>
  
  <p>I see that it will throw an error if there is no username/password param:</p>
  
  <pre><code>if (!options.use_unauthenticated) {
      if (!options.username || !options.password) {
        throw new Error('Argument error: username and password are required unless use_unauthenticated is set');
      }
  </code></pre>
  
  <p>How am I supposed to use IAM if the username/password is a requirement of the <a href="https://github.com/watson-developer-cloud/node-sdk#iam" rel="nofollow noreferrer">watson-developer-cloud</a> tooling? Is this an issue with the node module or am I doing something wrong?</p>
  
  <p>I am using watson-developer-cloud@2.42.0</p>