title: What is the meaning of viewer field in GraphQL?
body: <p>What is the purpose of root query field <code>viewer</code> in GraphQL?</p>
  
  <p>Based on <a href="https://medium.com/the-graphqlhub/graphql-and-authentication-b73aed34bbeb#.cpmrcqcyt">this article</a>, <code>viewer</code> could be used to accept a token parameter so we can see who is currently logged in.</p>
  
  <p>How should I implement it?</p>