code: function _auth( request, options, forceAuthentication ) {
  	// If we're not supposed to authenticate, don't even start
  	if ( ! forceAuthentication && ! options.auth && ! options.nonce ) {
  		return request;
  	}
  
  	// Enable nonce in options for Cookie authentication http://wp-api.org/guides/authentication.html
  	if ( options.nonce ) {
  		request.set( 'X-WP-Nonce', options.nonce );
  		return request;
  	}
  
  	// Retrieve the username & password from the request options if they weren't provided
  	const username = options.username;
  	const password = options.password;
  
  	// If no username or no password, can't authenticate
  	if ( ! username || ! password ) {
  		return request;
  	}
  
  	// Can authenticate: set basic auth parameters on the request
  	return request.auth( username, password );
  }
docs: Conditionally set basic authentication on a server request object.
  
  @method _auth
  @private
  @param {Object} request A superagent request object
  @param {Object} options A WPRequest _options object
  @param {Boolean} forceAuthentication whether to force authentication on the request
  @param {Object} A superagent request object, conditionally configured to use basic auth