express-session

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Installation

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

$ npm install express-session

API

var session = require('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

express-session accepts these properties in the options object.

cookie

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

In addition to providing a static object, you can also pass a callback function to dynamically generate the cookie options for each request. The callback receives the req object as its argument and should return an object containing the cookie settings.

var app = express()
app.use(session({
  secret: 'keyboard cat',
  resave: false,
  saveUninitialized: true,
  cookie: function(req) {
    var match = req.url.match(/^\/([^/]+)/);
    return {
      path: match ? '/' + match[1] : '/',
      httpOnly: true,
      secure: req.secure || false,
      maxAge: 60000
    }
  }
}))

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.partitioned

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

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.

More information about can be found in the proposal.

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.priority

Specifies the string to be the value for the [Priority Set-Cookie attribute][rfc-west-cookie-priority-00-4.1].

• 'low' will set the Priority attribute to Low.
• 'medium' will set the Priority attribute to Medium, the default priority when not set.
• 'high' will set the Priority attribute to High.

More information about the different priority levels can be found in [the specification][rfc-west-cookie-priority-00-4.1].

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.

cookie.sameSite

Specifies the boolean or string to be the value for the SameSite Set-Cookie attribute. By default, this is false.

• 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.
• 'auto' will set the SameSite attribute to None for secure connections and Lax for non-secure connections.

More information about the different enforcement levels can be found in [the specification][rfc-6265bis-03-4.1.2.7].

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.

The cookie.sameSite option can also be set to the special value 'auto' to have this setting automatically match the determined security of the connection. When the connection is secure (HTTPS), the SameSite attribute will be set to None to enable cross-site usage. When the connection is not secure (HTTP), the SameSite attribute will be set to Lax for better security while maintaining functionality. This is useful when the Express "trust proxy" setting is properly setup to simplify development vs production configuration, particularly for SAML authentication scenarios.

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 true, but using the default has been deprecated, as the default will change in the future. Please research into this setting and choose what is appropriate to your use-case. Typically, you'll want 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 conjunction 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. Choosing false is useful for implementing login sessions, reducing server storage usage, or complying with laws that require permission before setting a cookie. Choosing false will also help with race conditions where a client makes multiple parallel requests without a session.

The default value is true, but using the default has been deprecated, as the default will change in the future. Please research into this setting and choose what is appropriate to your use-case.

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

Required option

This is the secret used to sign the session ID cookie. The secret can be any type of value that is supported by Node.js crypto.createHmac (like a string or a Buffer). This can be either 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 val