title: Is doOnCompleted a valid way to handle token authentication?
body: <p>I was wondering about token authentication with Retrofit/RxJava.
  I was refactoring my code to use a DataManager, such that the activity evokes a method in the presenter, the presenter subscribes to the datamanager.getTrips which is then responsible for the call to the api.</p>
  
  <p>I want to make sure that my accesstoken is valid, and if it is not generate it first and then complete the task. Would doOnCompleted be a good way of achieving this or is there a better way?</p>
  
  <pre><code>/*In DataManager, service is the REST Interface*/
  public Observable&lt;VtTripResponseModel&gt; getTrips(final String start, final String end, final String time, final String date){
          if(accessToken.isValid()){
              return service.getTrip(accessToken.getAccessString(),start,end,time,date,JSON_PARAM);
          }
          else{
              generateAccessToken().doOnCompleted(new Action0() {
                  @Override
                  public void call() {
                      getTrips(start, end, time, date);
                  }
              });
          }
  
  /*What do I return here? Since this will not be reached*/
      }
  </code></pre>