title: Firebase Auth. How to design many users can login to one main company account.?
body: <p>Hi I have used Firebase over 2years and really loveit.</p>
  
  <p>I want to craete a new app for company. and use Firebase Auth.
  I understand for game 1user per :  1 game record data.   It is easy. i know how to do it.</p>
  
  <p>BUT enterprise app LIKE Slack.com;<br>
  many users link to one company data with own login.</p>
  
  <pre><code>ex ;   {{company}}.slack.com  =&gt;  user1, user2, user3
      or www.slack.com/{{company}} =&gt;  user1, user2, user3
      or www.slack.com  [only] =&gt;  user1, user2, user3, [link =&gt; 1company data]
  </code></pre>
  
  <p>So it means one company account and have many users link to it with permission.</p>
  
  <p>My questions are </p>
  
  <ol>
  <li><p>Are there any best practice for company login ?</p></li>
  <li><p>It is better if it can only with username login(not email login for users).</p></li>
  </ol>