code: function parseAuthorizationHeader (req, res, next) {
    // parse the header if it's present in the request
    if (req.headers && req.headers.authorization) {
      var components = req.headers.authorization.split(' ')
      var scheme = components[0]
      var credentials = components[1]
  
      // ensure the correct number of components
      if (components.length !== 2) {
        return next(new UnauthorizedError({
          error: 'invalid_request',
          error_description: 'Invalid authorization header',
          statusCode: 400
        }))
      }
  
      // ensure the scheme is valid
      if (!scheme.match(/Basic|Bearer|Digest/i)) {
        return next(new UnauthorizedError({
          error: 'invalid_request',
          error_description: 'Invalid authorization scheme',
          statusCode: 400
        }))
      }
  
      req.authorization = {
        scheme: scheme,
        credentials: credentials
      }
  
    // otherwise add an empty authorization object
    } else {
      req.authorization = {}
    }
  
    next()
  }
docs: Parse Authorization Header