title: request.getRemoteUser returns null
body: <p>I have deployed a web in tomcat 7.0.29, generate the HttpServletRequest's Object request,
  when I used the request like belows:</p>
  
  <pre><code> String remoteUser=request.getRemoteUser();
  </code></pre>
  
  <p>The remoteUser will be null. Any way to get remote use?</p>
  
  <p>I have refered to the link
  <a href="https://stackoverflow.com/questions/12446257/accessing-username-with-getremoteuser-when-using-custom-authentication-filter">Accessing username with getRemoteUser() when using custom authentication filter</a> ,but cannot resolve this error...</p>