code: public String getShareKey(Credentials credentials) {
  
          // Pull associated HTTP request
          HttpServletRequest request = credentials.getRequest();
          if (request == null)
              return null;
  
          // Retrieve the share key from the request
          return request.getParameter(SHARE_KEY_NAME);
  
      }
docs: Returns the share key contained within the given credentials. If there is
  no such share key, null is returned.
  
  @param credentials
  The credentials from which the share key should be retrieved.
  
  @return
  The share key contained within the given credentials, or null if
  the credentials do not contain a share key.