Vary middleware

auth.js

'use strict';

const USER_ID_HEADER = 'Fastly-Auth-UserID';
const RANK_HEADER = 'Fastly-Auth-Rank';
const TOKEN_HEADER = 'Fastly-Auth-Token';

module.exports = () => {
  return (req, res, next) => {
    const uid = req.get(USER_ID_HEADER);
    const rank = req.get(RANK_HEADER);
    const token = req.get(TOKEN_HEADER);

    req.auth = {
      isLoggedIn() {
        res.set('vary', RANK_HEADER);
        return rank !== undefined && rank !== 'anonymous';
      },
      getRank() {
        res.set('vary', RANK_HEADER);
        return rank;
      },
      getUserId() {
        res.set('vary', USER_ID_HEADER);
        return uid;
      },
      getToken() {
        res.set('vary', TOKEN_HEADER);
        return token;
      }
    };

    next();
  };
};

vary.js

module.exports = () => {
  return (req, res, next) => {
    const resSet = res.set;
    const headers = {
      'vary': new Set()
    };

    const modifyHeader = (name, val, mode) => {
      name = name.toLowerCase();
      if (name in headers) {
        val = Array.isArray(val) ? val : val.split(',');
        val.forEach(item => {
          headers[name][mode](item.trim().toLowerCase());
        });
        val = Array.from(headers[name]).join(', ');
      }
      return val ? resSet.call(res, name, val) : res.removeHeader(name);
    };

    // Caution: These exported functions use the res scope so
    // cannot be implemented as arrow functions
    res.set = function (name, val) {
      if (arguments.length === 2 && typeof name === 'string') {
        return modifyHeader(name, val, 'add');
      } else if (arguments.length === 1 && typeof name === 'object') {
        Object.keys(name).forEach(key => modifyHeader(key, name[key], 'add'));
      } else {
        return resSet.call(res, name, val);
      }
    };

    res.unset = function (name, val) {
      if (arguments.length === 2 && typeof arguments[0] === 'string') {
        return modifyHeader(name, val, 'delete');
      } else if (arguments.length === 1 && typeof arguments[0] === 'string') {
        return res.removeHeader(name);
      }
      throw new Error('Invalid call to res.unset');
    };

    next();
  };
};