node-session-handler

Module provides a way of handling Companies House sessions.

Module offers the following artifacts:

- Session that reflects structure of the session including elements of Single Sign-On
- SessionStore that is responsible for reading and writing session data from / to database taking care of data encoding / decoding
- SessionMiddleware that provides easy to use express.js middleware reading session based on the request cookie

Compatible Node.js Versions

This package has been upgraded to be compatible with Node v24. Presently, it's backward compatible with v20 and v18 but compatibility is primarily required for v24 as all CH Node services are in the process of being upgraded to v24.

Prerequisite

Module requires request.cookies map to be populated with an object keyed by the cookie names. It can be achieved by use of cookie-parser module.

In short run npm install cookie-parser command to install dependency and add the following snipped to the application to apply cookie parsing middleware:

``$typescript
import * as cookieParser from 'cookie-parser'
...
app.use(cookieParser())
`

Note: Cookie parsing must happen before request is passed to session middleware.

How to use it

To bring this module as dependency please add the following fragment to package.json:

`$json
"@companieshouse/node-session-handler": "~4.1.0"
`

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The session class is a wrapper around the raw session data: ISession (as retrieved from accounts after signing in).

To keep the ISession type consistent, we added an extra field called extra_data (SessionKey.ExtraData) to store any data that apps might need in the session making session itself extensible.

The class provides these methods:

- get(key: SessionKey): T | undefined - allows retrieving session data for keys defined in the SessionKey enum that represents all possible types than can be retrieved from the session
- getExtraData(key: string): T | undefined - allows retrieving session data populated by the applications
- setExtraData(key: string, val: T): void - allows amending session data used by the applications by replacing existing value (if present)
- deleteExtraData(key: string): boolean - deletes a key from the session data populated by an application (if exists)
- verify = (): void - ensures that the session is valid i.e. contains the right fields, and it's not expired

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Session store offers a way to load SessionStore.load, store SessionStore.store and delete SessionStore.delete session from database without worrying about data encoding or decoding.

All above methods take instance of Cookie class which holds combination of session ID and signature. Use of that argument type helps to ensure that database operations are only performed for verified session identifiers.

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Session middleware provides convenient integration point for express.js applications. Middleware does:

1. read cookie value from request HTTP headers
2. verify cookie signature if cookie is present
3. load session from store using verified cookie if present
4. sets verified session in request scope
5. stores session in store on request end if session data changed

Express.js applications wishing to introduce session handling should register middleware in the following way:

`$javascript

const sessionStore = new SessionStore(new Redis(redis://${process.env.CACHE_SERVER}))
const middleware = SessionMiddleware({
cookieName: process.env.COOKIE_NAME,
cookieDomain: process.env.COOKIE_DOMAIN,
cookieSecureFlag: process.env.COOKIE_SECURE_ONLY,
cookieTimeToLiveInSeconds: process.env.DEFAULT_SESSION_EXPIRATION,
cookieSecret: process.env.COOKIE_SECRET
}, sessionStore)

app.use(middleware)
`

Such application will then have access to session instance via request.session as long as __SID cookie is set to correct value.

There is also an option to have not authenticated sessions without sign-in info. In such cases middleware creates empty session as long as no valid session was found in the request.

To enable support for non authenticated sessions pass true as a last argument to the middleware factory function e.g. SessionMiddleware(config, sessionStore, true).

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Convenient Express middleware function which ensures requests contain the
Session ID Cookie and forces a redirect if not. This is necessary if subsequent
middlewares require the Cookie to be present in the request.

Should be used alongside the SessionMiddleware and be placed following it
in the chain of middleware functions.

Should be used in the following way:

`javascript
// Create CookieConfig as required
const cookieConfig = { ... };

// Create sessionMiddleware using same cookie config, refer to previous section
// for explicit instructions
const sessionMiddleware = ...;
const ensureSessionCookiePresentMiddleware =
EnsureSessionCookiePresentMiddleware({
// Ensure use the same cookie name as session, spreading cookie config
// will accomplish this
...cookieConfig,
// Supply values for redirectHeaderName and redirectHeaderValue
// to customise the header which is used to validate the redirected
// request. (Defaults to name: x-redirection-count value: 1)
redirectHeaderName: "not-redirect",
redirectHeaderValue: "not-true",
})

app.use(sessionMiddleware)
app.use(ensureSessionCookiePresentMiddleware)
`

Development

Module requires dependencies that can be installed via npm install command.

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Code is linted using ts-lint which can be run via npm run lint command.

Tests in turn can be run via npm test` command.