Question

Simple cookie-based session middleware.

A user session can be stored in two main ways with cookies: on the server or on the client. This module stores the session data on the client within a cookie, while a module like express-session stores only a session identifier on the client within a cookie and stores the session data on the server, typically in a database.

The following points can help you choose which to use:

• cookie-session does not require any database / resources on the server side, though the total session data cannot exceed the browser’s max cookie size.
• cookie-session can simplify certain load-balanced scenarios.
• cookie-session can be used to store a “light” session and include an identifier to look up a database-backed secondary store to reduce database lookups.

Install

This is a Node.js module available through the npm registry. Installation is done using the npm install command:

$ npm install cookie-session

API

var cookieSession = require('cookie-session')
var express = require('express')

var app = express()

app.use(cookieSession({
  name: 'session',
  keys: [/* secret keys */],

  // Cookie Options
  maxAge: 24 * 60 * 60 * 1000 // 24 hours
}))

cookieSession(options)

Create a new cookie session middleware with the provided options. This middleware will attach the property session to req, which provides an object representing the loaded session. This session is either a new session if no valid session was provided in the request, or a loaded session from the request.

The middleware will automatically add a Set-Cookie header to the response if the contents of req.session were altered. Note that no Set-Cookie header will be in the response (and thus no session created for a specific user) unless there are contents in the session, so be sure to add something to req.session as soon as you have identifying information to store for the session.

Options

Cookie session accepts these properties in the options object.

name

The name of the cookie to set, defaults to session.

keys

The list of keys to use to sign & verify cookie values, or a configured Keygrip instance. Set cookies are always signed with keys[0], while the other keys are valid for verification, allowing for key rotation. If a Keygrip instance is provided, it can be used to change signature parameters like the algorithm of the signature.

secret

A string which will be used as single key if keys is not provided.

Cookie Options

Other options are passed to cookies.get() and cookies.set() allowing you to control security, domain, path, and signing among other settings.

The options can also contain any of the following (for the full list, see cookies module documentation:

• maxAge: a number representing the milliseconds from Date.now() for expiry
• expires: a Date object indicating the cookie’s expiration date (expires at the end of session by default).
• path: a string indicating the path of the cookie (/ by default).
• domain: a string indicating the domain of the cookie (no default).
• sameSite: a boolean or string indicating whether the cookie is a “same site” cookie (false by default). This can be set to 'strict', 'lax', or true (which maps to 'strict').
• secure: a boolean indicating whether the cookie is only to be sent over HTTPS (false by default for HTTP, true by default for HTTPS). If this is set to true and Node.js is not directly over a TLS connection, be sure to read how to setup Express behind proxies or the cookie may not ever set correctly.
• httpOnly: a boolean indicating whether the cookie is only to be sent over HTTP(S), and not made available to client JavaScript (true by default).
• signed: a boolean indicating whether the cookie is to be signed (true by default). If this is true, another cookie of the same name with the .sig suffix appended will also be sent, with a 27-byte url-safe base64 SHA1 value representing the hash of cookie-name=cookie-value against the first Keygrip key. This signature key is used to detect tampering the next time a cookie is received.
• overwrite: a boolean indicating whether to overwrite previously set cookies of the same name (true by default). If this is true, all cookies set during the same request with the same name (regardless of path or domain) are filtered out of the Set-Cookie header when setting this cookie.

req.session

Represents the session for the given request.

.isChanged

Is true if the session has been changed during the request.

.isNew

Is true if the session is new.

.isPopulated

Determine if the session has been populated with data or is empty.

req.sessionOptions

Represents the session options for the current request. These options are a shallow clone of what was provided at middleware construction and can be altered to change cookie setting behavior on a per-request basis.

Destroying a session

To destroy a session simply set it to null:

req.session = null

Examples

Simple view counter example

var cookieSession = require('cookie-session')
var express = require('express')

var app = express()

app.set('trust proxy', 1) // trust first proxy

app.use(cookieSession({
  name: 'session',
  keys: ['key1', 'key2']
}))

app.get('/', function (req, res, next) {
  // Update views
  req.session.views = (req.session.views || 0) + 1

  // Write response
  res.end(req.session.views + ' views')
})

app.listen(3000)

Per-user sticky max age

var cookieSession = require('cookie-session')
var express = require('express')

var app = express()

app.set('trust proxy', 1) // trust first proxy

app.use(cookieSession({
  name: 'session',
  keys: ['key1', 'key2']
}))

// This allows you to set req.session.maxAge to let certain sessions
// have a different value than the default.
app.use(function (req, res, next) {
  req.sessionOptions.maxAge = req.session.maxAge || req.sessionOptions.maxAge
  next()
})

// ... your logic here ...

Extending the session expiration

This module does not send a Set-Cookie header if the contents of the session have not changed. This means that to extend the expiration of a session in the user’s browser (in response to user activity, for example) some kind of modification to the session needs be made.

var cookieSession = require('cookie-session')
var express = require('express')

var app = express()

app.use(cookieSession({
  name: 'session',
  keys: ['key1', 'key2']
}))

// Update a value in the cookie so that the set-cookie will be sent.
// Only changes every minute so that it's not sent with every request.
app.use(function (req, res, next) {
  req.session.nowInMinutes = Math.floor(Date.now() / 60e3)
  next()
})

// ... your logic here ...

Using a custom signature algorithm

This example shows creating a custom Keygrip instance as the keys option to provide keys and additional signature configuration.

var cookieSession = require('cookie-session')
var express = require('express')
var Keygrip = require('keygrip')

var app = express()

app.use(cookieSession({
  name: 'session',
  keys: new Keygrip(['key1', 'key2'], 'SHA384', 'base64')
}))

// ... your logic here ...

Usage Limitations

Max Cookie Size

Because the entire session object is encoded and stored in a cookie, it is possible to exceed the maxium cookie size limits on different browsers. The RFC6265 specification recommends that a browser SHOULD allow

At least 4096 bytes per cookie (as measured by the sum of the length of the cookie’s name, value, and attributes)

In practice this limit differs slightly across browsers. See a list of browser limits here. As a rule of thumb don’t exceed 4093 bytes per domain.

If your session object is large enough to exceed a browser limit when encoded, in most cases the browser will refuse to store the cookie. This will cause the following requests from the browser to either a) not have any session information or b) use old session information that was small enough to not exceed the cookie limit.

If you find your session object is hitting these limits, it is best to consider if data in your session should be loaded from a database on the server instead of transmitted to/from the browser with every request. Or move to an alternative session strategy