Design for an application that works with multiple services

I have a java application that works with multiple services like "auth", "chat" and "agenda".

The application call first auth for login, then use chat and agenta simultanly, maybe concurency.

       _
       |
       V
      auth
       |
       V
 --------------
 |            |
 V            V          
chat        agenda

What design should be adopted for application? How should look like main?