title: How to use a provider inside of another provider in Flutter
body: <p>I want to create an app that has an <code>authentication service</code> with different permissions and functions (e.g. messages) depending on the user role. </p>
  
  <p>So I created one <code>Provider</code> for the user and login management and another one for the messages the user can see. </p>
  
  <p>Now, I want to fetch the messages (once) when the user logs in. In <code>Widgets</code>, I can access the Provider via <code>Provider.of&lt;T&gt;(context)</code> and I guess that's a kind of <code>Singleton</code>. But how can I access it from another class (in this case another Provider)?</p>