title: Unable to use credentials to publish or install with yarn
body: <p>I'm relatively recently researching npm and yarn for managing javascript packages.  For various reasons (mostly obvious to yarn users) I think I would like to settle on yarn long term.  For the past several days, while playing, after my first use of <code>yarn login</code>I have had no trouble using <code>yarn publish</code> and <code>yarn add</code> (or <code>yarn upgrade</code>) to publish and install private scoped modules through the npm registry.  Today, when starting to work on a full build package, used <code>yarn logout</code> to logout, and then tried logging in again with <code>yarn login</code>.  But now, I am completely unable to use <code>yarn publish</code> to publish my packages or <code>yarn install</code> to install any privately scoped packages.  npm works fine.</p>
  
  <p>I'm baffled as to what has gone wrong.</p>
  
  <p>Somehow the authentication is not working correctly and I don't see what I have done to break it.  That said, I don't understand it very well either.</p>