@saasform/express-session

!! IMPORTANT !! This library is in alpha, not yet recommended for production - please help us battle test it !!

This is express-session by Saasform, a drop-in replacement of express-session with enhanced security.

Compared to the original express-session, our re-implementation:

1. Prevents session fixation (e.g., when a user logs in a new token is emitted)
2. Guarantees that destroyed sessions can't be re-saved (e.g., a logged out session can't become alive again)
3. Reduces the impact of data theft from the store (stores hash(sessId) instead of sessId)
4. Improves upon deprecated default config options

In addition, it's a drop-in replacement in the sense that you can replace the npm package and all existig/active sessions will be transparently upgraded from the original to the new format, without logging users out.

Our implementation uses JWT tokens for session tokens. This lets you store some data that changes infrequently (e.g., user id, roles...) with the JWT token, while you can still maintain the full flexibility of your store (e.g., for counters). We expect tokens to be passed as secure, http-only cookies. We use public key cryptography such that you can have a single service issueing tokens but multiple services verifying them (with only public key access, no private key).

Features:

• [x] Pass all original express-session tests (only changes are the default config values)
• [x] Add keys option with public/private keys
• [x] Add jwtFromReq option to return content of JWT token
• [x] Issue a new JWT token when the result of jwtFromReq changes (e.g., set a user id)
• [x] Transparently upgrade existing original Express sessions (retrieve data from db with old id, generate JWT token, store data with new id)
• [x] Use hash(sessId) instead of sessId as primary key in the store
• [x] Prevent race condition that would re-save a destroyed session in MemoryStore
• [x] Support key rotation (sign with the latest private key, try to verify with older public keys as well)
• [ ] Add async keys provider (retrieve keys from req and/or token)
• [ ] Support verifier only mode (public keys only, no private key)
• [ ] Richer interface for stores

Installation

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

$ npm install @saasform/express-session

API

var session = require('@saasform/express-session')

session(options)

Create a session middleware with the given options.

Note Session data is not saved in the cookie itself, just the session ID. Session data is stored server-side.

Note Since version 1.5.0, the cookie-parser middleware no longer needs to be used for this module to work. This module now directly reads and writes cookies on req/res. Using cookie-parser may result in issues if the secret is not the same between this module and cookie-parser.

Warning The default server-side session storage, MemoryStore, is purposely not designed for a production environment. It will leak memory under most conditions, does not scale past a single process, and is meant for debugging and developing.

For a list of stores, see compatible session stores.

Options

@saasform/express-session accepts these properties in the options object.

keys

Required option

Set the private and public key(s) to sign/verify the JWT tokens.

Keys should either be an object with public and private properties, or an array of such objects. When an array, the first element is the most recent key. For older keys only the public key is required, the private key can be omitted.

Examples:

keys: { public: '...', private: '...' }

or

keys: [{ public: 'latest', private: '...' }, { public: 'old1' }, { public: 'old2' }]

We currenlty use the ES256 algorithm. Keys can be generated with:

openssl ecparam -name secp256k1 -genkey -noout -out private-key.pem
openssl ec -in ec-secp256k1-priv-key.pem -pubout > public-key.pem

jwtFromReq

Function to call to generate the payload of a JWT token. Provide a function that returns an object that will be used as payload. The function is given req as the first argument if you want to use some value attached to req when generating the JWT token.

Example:

function jwtFromReq(req) {
  return req.user ? {
    user_id: req.user.id,
    roles: ['user', 'editor']
  } : null
}

Options (same as the original express-session)

@saasform/express-session also accepts these properties as the original express-session.

cookie

Settings object for the session ID cookie. The default value is { path: '/', httpOnly: true, secure: false, maxAge: null }.

The following are options that can be set in this object.

cookie.domain

Specifies the value for the Domain Set-Cookie attribute. By default, no domain is set, and most clients will consider the cookie to apply to only the current domain.

cookie.expires

Specifies the Date object to be the value for the Expires Set-Cookie attribute. By default, no expiration is set, and most clients will consider this a "non-persistent cookie" and will delete it on a condition like exiting a web browser application.

Note If both expires and maxAge are set in the options, then the last one defined in the object is what is used.

Note The expires option should not be set directly; instead only use the maxAge option.

cookie.httpOnly

Specifies the boolean value for the HttpOnly Set-Cookie attribute. When truthy, the HttpOnly attribute is set, otherwise it is not. By default, the HttpOnly attribute is set.

Note be careful when setting this to true, as compliant clients will not allow client-side JavaScript to see the cookie in document.cookie.

cookie.maxAge

Specifies the number (in milliseconds) to use when calculating the Expires Set-Cookie attribute. This is done by taking the current server time and adding maxAge milliseconds to the value to calculate an Expires datetime. By default, no maximum age is set.

Note If both expires and maxAge are set in the options, then the last one defined in the object is what is used.

cookie.path

Specifies the value for the Path Set-Cookie. By default, this is set to '/', which is the root path of the domain.

cookie.sameSite

Specifies the boolean or string to be the value for the SameSite Set-Cookie attribute.

• true will set the SameSite attribute to Strict for strict same site enforcement.
• false will not set the SameSite attribute.
• 'lax' will set the SameSite attribute to Lax for lax same site enforcement.
• 'none' will set the SameSite attribute to None for an explicit cross-site cookie.
• 'strict' will set the SameSite attribute to Strict for strict same site enforcement.

More information about the different enforcement levels can be found in the specification.

Note This is an attribute that has not yet been fully standardized, and may change in the future. This also means many clients may ignore this attribute until they understand it.

Note There is a draft spec that requires that the Secure attribute be set to true when the SameSite attribute has been set to 'none'. Some web browsers or other clients may be adopting this specification.

cookie.secure

Specifies the boolean value for the Secure Set-Cookie attribute. When truthy, the Secure attribute is set, otherwise it is not. By default, the Secure attribute is not set.

Note be careful when setting this to true, as compliant clients will not send the cookie back to the server in the future if the browser does not have an HTTPS connection.

Please note that secure: true is a recommended option. However, it requires an https-enabled website, i.e., HTTPS is necessary for secure cookies. If secure is set, and you access your site over HTTP, the cookie will not be set. If you have your node.js behind a proxy and are using secure: true, you need to set "trust proxy" in express:

var app = express()
app.set('trust proxy', 1) // trust first proxy
app.use(session({
  secret: 'keyboard cat',
  resave: false,
  saveUninitialized: true,
  cookie: { secure: true }
}))

For using secure cookies in production, but allowing for testing in development, the following is an example of enabling this setup based on NODE_ENV in express:

var app = express()
var sess = {
  secret: 'keyboard cat',
  cookie: {}
}

if (app.get('env') === 'production') {
  app.set('trust proxy', 1) // trust first proxy
  sess.cookie.secure = true // serve secure cookies
}

app.use(session(sess))

The cookie.secure option can also be set to the special value 'auto' to have this setting automatically match the determined security of the connection. Be careful when using this setting if the site is available both as HTTP and HTTPS, as once the cookie is set on HTTPS, it will no longer be visible over HTTP. This is useful when the Express "trust proxy" setting is properly setup to simplify development vs production configuration.

genid

Function to call to generate a new session ID. Provide a function that returns a string that will be used as a session ID. The function is given req as the first argument if you want to use some value attached to req when generating the ID.

The default value is a function which uses the uid-safe library to generate IDs.

NOTE be careful to generate unique IDs so your sessions do not conflict.

app.use(session({
  genid: function(req) {
    return genuuid() // use UUIDs for session IDs
  },
  secret: 'keyboard cat'
}))

name

The name of the session ID cookie to set in the response (and read from in the request).

The default value is 'connect.sid'.

Note if you have multiple apps running on the same hostname (this is just the name, i.e. localhost or 127.0.0.1; different schemes and ports do not name a different hostname), then you need to separate the session cookies from each other. The simplest method is to simply set different names per app.

proxy

Trust the reverse proxy when setting secure cookies (via the "X-Forwarded-Proto" header).

The default value is undefined.

• true The "X-Forwarded-Proto" header will be used.
• false All headers are ignored and the connection is considered secure only if there is a direct TLS/SSL connection.
• undefined Uses the "trust proxy" setting from express

resave

Forces the session to be saved back to the session store, even if the session was never modified during the request. Depending on your store this may be necessary, but it can also create race conditions where a client makes two parallel requests to your server and changes made to the session in one request may get overwritten when the other request ends, even if it made no changes (this behavior also depends on what store you're using).

The default value is false.

How do I know if this is necessary for my store? The best way to know is to check with your store if it implements the touch method. If it does, then you can safely set resave: false. If it does not implement the touch method and your store sets an expiration date on stored sessions, then you likely need resave: true.

rolling

Force the session identifier cookie to be set on every response. The expiration is reset to the original maxAge, resetting the expiration countdown.

The default value is false.

With this enabled, the session identifier cookie will expire in maxAge since the last response was sent instead of in maxAge since the session was last modified by the server.

This is typically used in conjuction with short, non-session-length maxAge values to provide a quick timeout of the session data with reduced potential of it occurring during on going server interactions.

Note When this option is set to true but the saveUninitialized option is set to false, the cookie will not be set on a response with an uninitialized session. This option only modifies the behavior when an existing session was loaded for the request.

saveUninitialized

Forces a session that is "uninitialized" to be saved to the store. A session is uninitialized when it is new but not modified.

The default value is false.

Note if you are using Session in conjunction with PassportJS, Passport will add an empty Passport object to the session for use after a user is authenticated, which will be treated as a modification to the session, causing it to be saved. This has been fixed in PassportJS 0.3.0

secret

This is the secret used to sign the session ID cookie by the original Express session.

This option is required to upgrade existing Express sessions into the new format.

This can be either a string for a single secret, or an array of multiple secrets. If an array of secrets is provided, only the first element will be used to sign the session ID cookie, while all the elements will be considered when verifying the signature in requests. The secret itself should be not easily parsed by a human and would best be a random set of characters. A best practice may include:

• The use of environment variables to store the secret, ensuring the secret itself does not exist in your repository.
• Periodic updates of the secret, while ensuring the previous secret is in the array.

Using a secret that cannot be guessed will reduce the ability to hijack a session to only guessing the session ID (as determined by the genid option).

Changing the secret value will invalidate all existing sessions. In order to rotate the secret without invalidating sessions, provide an array of secrets, with the new secret as first element of the array, and including previous secrets as the later elements.

store

The session store instance, defaults to a new MemoryStore instance.

unset

Control the result of unsetting req.session (through delete, setting to null, etc.).

The default value is 'keep'.

• 'destroy' The session will be destroyed (deleted) when the response ends.
• 'keep' The session in the store will be kept, but modifications made during the request are ignored and not saved.

req.session

To store or access session data, simply use the request property req.session, which is (generally) serialized as JSON by the store, so nested objects are typically fine. For example below is a user-specific view counter:

// Use the session middleware
app.use(session({ secret: 'keyboard cat', cookie: { maxAge: 60000 }}))

// Access the session as req.session
app.get('/', function(req, res, next) {
  if (req.session.views) {
    req.session.views++
    res.setHeader('Content-Type', 'text/html')
    res.write('<p>views: ' + req.session.views + '</p>')
    res.write('<p>expires in: ' + (req.session.cookie.maxAge / 1000) + 's</p>')
    res.end()
  } else {
    req.session.views = 1
    res.end('welcome to the session demo. refresh!')
  }
})

Session.regenerate(callback)

To regenerate the session simply invoke the method. Once complete, a new SID and Session instance will be initialized at req.session and the callback will be invoked.

req.session.regenerate(function(err) {
  // will have a new session here
})

Session.destroy(callback)

Destroys the session and will unset the req.session property. Once complete, the callback will be invoked.

req.session.destroy(function(err) {
  // cannot access session here
})

Session.reload(callback)

Reloads the session data from the store and re-populates the req.session object. Once complete, the callback will be invoked.

req.session.reload(function(err) {
  // session updated
})

Session.save(callback)

Save the session back to the store, replacing the contents on the store with the contents in memory (though a store may do something else--consult the store's documentation for exact behavior).

This method is automatically called at the end of the HTTP response if the session data has been altered (though this behavior can be altered with various options in the middleware constructor). Because of this, typically this method does not need to be called.

There are some cases where it is useful to call this method, for example, redirects, long-lived requests or in WebSockets.

req.session.save(function(err) {
  // session saved
})

Session.touch()

Updates the .maxAge property. Typically this is not necessary to call, as the session middleware does this for you.

req.session.id

Each session has a unique ID associated with it. This property is an alias of req.sessionID and cannot be modified. It has been added to make the session ID accessible from the session object.

req.session.jwt

The content of the JWT token, parsed at the beginning of a request. Add arbitrary data via the jwtFromReq option.

req.session.cookie

Each session has a unique cookie object accompany it. This allows you to alter the session cookie per visitor. For example we can set req.session.cookie.expires to false to enable the cookie to remain for only the duration of the user-agent.

Cookie.maxAge

Alternatively req.session.cookie.maxAge will return the time remaining in milliseconds, which we may also re-assign a new value to adjust the .expires property appropriately. The following are essentially equivalent

var hour = 3600000
req.session.cookie.expires = new Date(Date.now() + hour)
req.session.cookie.maxAge = hour

For example when maxAge is set to 60000 (one minute), and 30 seconds has elapsed it will return 30000 until the current request has completed, at which time req.session.touch() is called to reset req.session.cookie.maxAge to its original value.

req.session.cookie.maxAge // => 30000

Cookie.originalMaxAge

The req.session.cookie.originalMaxAge property returns the original maxAge (time-to-live), in milliseconds, of the session cookie.

req.sessionID

To get the ID of the loaded session, access the request property req.sessionID. This is simply a read-only value set when a session is loaded/created.

Session Store Implementation

Every session store must be an EventEmitter and implement specific methods. The following methods are the list of required, recommended, and optional.

• Required methods are ones that this module will always call on the store.
• Recommended methods are ones that this module will call on the store if available.
• Optional methods are ones this module does not call at all, but helps present uniform stores to users.

For an example implementation view the connect-redis repo.

store.all(callback)

Optional

This optional method is used to get all sessions in the store as an array. The callback should be called as callback(error, sessions).

store.destroy(sid, callback)

Required

This required method is used to destroy/delete a session from the store given a session ID (sid). The callback should be called as callback(error) once the session is destroyed.

store.clear(callback)

Optional

This optional method is used to delete all sessions from the store. The callback should be called as callback(error) once the store is cleared.

store.length(callback)

Optional

This optional method is used to get the count of all sessions in the store. The callback should be called as callback(error, len).

store.get(sid, callback)

Required

This required method is used to get a session from the store given a session ID (sid). The callback should be called as callback(error, session).

The session argument should be a session if found, otherwise null or undefined if the session was not found (and there was no error). A special case is made when error.code === 'ENOENT' to act like callback(null, null).

store.set(sid, session, callback)

Required

This required method is used to upsert a session into the store given a session ID (sid) and session (session) object. The callback should be called as callback(error) once the session has been set in the store.

store.touch(sid, session, callback)

Recommended

This recommended method is used to "touch" a given session given a session ID (sid) and session (session) object. The callback should be called as callback(error) once the session has been touched.

This is primarily used when the store will automatically delete idle sessions and this method is used to signal to the store the given session is active, potentially resetting the idle timer.

Compatible Session Stores

For a complete list of compatible stores see the original docs. Any store that works with express-session should work unmodified with our library.

We recommend the following stores because they enforce that destroyed sessions can't be re-saved (e.g., a logged out session can't become alive again). Please make a PR to list additional stores.

connect-typeorm A TypeORM-based session store.

Example

A simple example using @saasform/express-session to store page views for a user.

var express = require('express')
var parseurl = require('parseurl')
var session = require('@saasform/express-session')

var app = express()

app.use(session({
  secret: 'keyboard cat',  // to upgrade existing Express sessions
  keys: {
    public: '-----BEGIN PUBLIC KEY-----\nMFYwEAYHKoZIzj0CAQYFK4EEAAoDQgAEDXMuNS4pyqkpZwij+UCcTPVStZHmG39D\nP1V7qaPCfc0ewXXbcEaJiarqjHOM5a6SVivCaUdJj+25tjMk4sPchQ==\n-----END PUBLIC KEY-----',
    private: '-----BEGIN PRIVATE KEY-----\nMIGEAgEAMBAGByqGSM49AgEGBSuBBAAKBG0wawIBAQQgvK1dk5M81nax8lQxpbWo\nsB1oK9YAqRP7MwWc7wDne8ehRANCAAQNcy41LinKqSlnCKP5QJxM9VK1keYbf0M/\nVXupo8J9zR7BddtwRomJquqMc4zlrpJWK8JpR0mP7bm2MyTiw9yF\n-----END PRIVATE KEY-----'
  },
}))

app.use(function (req, res, next) {
  if (!req.session.views) {
    req.session.views = {}
  }

  // get the url pathname
  var pathname = parseurl(req).pathname

  // count the views
  req.session.views[pathname] = (req.session.views[pathname] || 0) + 1

  next()
})

app.get('/foo', function (req, res, next) {
  res.send('you viewed this page ' + req.session.views['/foo'] + ' times')
})

app.get('/bar', function (req, res, next) {
  res.send('you viewed this page ' + req.session.views['/bar'] + ' times')
})

app.listen(3000);

Debugging

This module uses the debug module internally to log information about session operations.

To see all the internal logs, set the DEBUG environment variable to express-session when launching your app (npm start, in this example):

$ DEBUG=express-session npm start

On Windows, use the corresponding command;

> set DEBUG=express-session & npm start

License

MIT