title: Using JWT - is it fine to authenticate user with the subject being their email?
body: <p>I'm new to authentication, and just trying out JWT authentication on a small express app.</p>
  
  <p>I've got a user authentication setup using JWTs, and I'm using the subject as the user's email.</p>
  
  <p>Is this a good practice?</p>
  
  <p>If I decode the JWT on jwt.io, I see:</p>
  
  <pre><code>{
    "sub": "test_user_3@test.com",
    "iat": 1489963760,
    "exp": 1490568560
  }
  </code></pre>
  
  <p>Is that how it is supposed to work?  </p>