title: Allowing specific user write access
body: <p>I'm kind of stymied on my Firebase read/write rules. I wish I had a way to set break points as it's checking authentication (there isn't a way, is there?).</p>
  
  <p>My question is fairly simple and I feel like I should be able to understand it better.  I feel like most of stems from not understanding fully the rules.  This information is for a simple way to view products online and the owner needs to be able to add products.  So I want the world to be able to read and people who log in be able to write.</p>
  
  <p>My data looks like:</p>
  
  <pre><code>app
   Users
      email: xxx@xxx.com
   product
     0
       name: pizza
  </code></pre>
  
  <p>And my rules:</p>
  
  <pre><code> {
      "rules": {
        "product":{
          ".read": true,
          ".write":"root.child('Users').child(auth.uid).child('email').val() === 'testuser@test.com'"
        }
      }
  }
  </code></pre>
  
  <p>and I don't have a great grasp of what this means. I really just want to say, if the user is logged in, allow write capabilities.  I would have hoped I could so something like <code>".write": "auth"</code> meaning that if auth exists (user is logged in) then let him write.  But I'm clearly not fully understand how the rules work.  I'm using simple email/password authentication.</p>
  
  <p>How are these rules tested and how do I pass parameters to them?</p>