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Summary

Existing encrypted session objects from connect-mongo v3.2.0 remain over-stringified when decrypted by v4.4.1, as described in #393.

Other information

Steps to reproduce:

(Minimal docker-compose project to reproduce the issue: https://github.com/pauldwaite/connect-mongo-issue-420)

1. Start an Express web app that creates a session using connect-mongo 3.2.0.
2. Visit the web app in a browser.
3. Stop the web app (but persist the session data)
4. Update the web app to use connect-mongo 4.4.1
5. Restart the web app
6. Refresh the browser

Expected behaviour

The session still exists, and works correctly.

Actual behaviour

connect-mongo throws an error:

Error: Unable to parse ciphertext object!
    at /workdir/node_modules/connect-mongo/build/main/lib/MongoStore.js:187:23
    at processTicksAndRejections (internal/process/task_queues.js:93:5)
    at async MongoStore.decryptSession (/workdir/node_modules/connect-mongo/build/main/lib/MongoStore.js:186:31)
    at async /workdir/node_modules/connect-mongo/build/main/lib/MongoStore.js:211:21
TypeError: Cannot read property 'expires' of undefined
    at MongoStore.Store.createSession (/workdir/node_modules/express-session/session/store.js:87:29)
    at inflate (/workdir/node_modules/express-session/index.js:368:13)
    at /workdir/node_modules/express-session/index.js:495:11
    at /workdir/node_modules/connect-mongo/build/main/lib/MongoStore.js:218:17
    at processTicksAndRejections (internal/process/task_queues.js:93:5)

Additional information

I added a breakpoint in the get method in kruptein, and the cipher text variable started like this:

"\"{\\\"hmac\\\":\\\"97d0b61cd19623a...

Which I thought looked a bit like the over-stringified session object referred to in issue #393.