title: Should I always use serviceAccountCredentials.createDelegated() when using service account?
body: <p>There is a service account with domain-wide delegation and I need to get a list of users from Workspace by means of Admin SDK / Directory Api.
  Should I always call <code>serviceAccountCredentials.createDelegated( delegatedUserEmail )</code> or similar ?  This means I has to know at least one user email before getting the list of users (emails). Is there workaround for specifying this email?</p>
  <pre><code>        final ServiceAccountCredentials serviceAccountCredentials = ServiceAccountCredentials
                  .fromPkcs8(
                          clientId,
                          clientEmail,
                          serviceAccountPkcs8Key,
                          serviceAccountPkcs8Id,
                          Arrays.asList(DirectoryScopes.ADMIN_DIRECTORY_USER_READONLY));
  
          final GoogleCredentials delegatedCredentials = serviceAccountCredentials.createDelegated(delegatedUserEmail);
  
          HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(delegatedCredentials);
  
          Directory directory = new Directory.Builder(
                  httpTransport, JSON_FACTORY, requestInitializer)
                  .setApplicationName(applicationName)
                  .build();
  </code></pre>
  <p>if I replace</p>
  <pre><code>final GoogleCredentials delegatedCredentials = serviceAccountCredentials.createDelegated(delegatedUserEmail);
  HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(delegatedCredentials);
  </code></pre>
  <p>with</p>
  <pre><code>HttpRequestInitializer requestInitializer = new HttpCredentialsAdapter(
  serviceAccountCredentials.createScoped(DirectoryScopes.ADMIN_DIRECTORY_USER_READONLY));
  </code></pre>
  <p>api responds an error:</p>
  <pre><code>com.google.api.client.googleapis.json.GoogleJsonResponseException: 400 Bad Request
  GET https://www.googleapis.com/admin/directory/v1/users?customer=my_customer&amp;maxResults=500
  {
    &quot;code&quot; : 400,
    &quot;errors&quot; : [ {
      &quot;domain&quot; : &quot;global&quot;,
      &quot;message&quot; : &quot;Invalid Input&quot;,
      &quot;reason&quot; : &quot;invalid&quot;
    } ],
    &quot;message&quot; : &quot;Invalid Input&quot;
  }
  </code></pre>