Update express-session and add custom returnTo property

[jackbravo]

Description

Also had some errores while updating express-session to latest release.

Specifically because of this change:

https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/express-session/index.d.ts#L202

from:

Reported here: https://github.com/DefinitelyTyped/DefinitelyTyped/issues/49484

Performance impact

Security impact

Checklist

• [ ] My code matches the project's code style and yarn lint:fix passes.
• [ ] I've added tests for the new feature, and yarn test passes.
• [ ] I have detailed the new feature in the relevant documentation.
• [ ] I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• [ ] If this is a breaking change I've explained why.

[benjie]

It seems the updates to the lockfile have caused cascading failures in the cypress tests. Apparently someone's not been adhering to semver :/ Those issues will need fixing before this can be merged; but I think that's probably beyond the scope of this PR. I'm going to leave this open until I have time to address this breakage, but thank you for sharing the fix :+1:

[lukeramsden]

From the Cypress screenshots it seems to be a trailing slash issue.

https://github.com/vercel/next.js/pull/15768

Could be this? Or related changes in Next.js 9.x. Looks like they've moved to a new trailing slash API, and then redirected the old exportTrailingSlash to enable to new one?

[lukeramsden]

exportTrailingSlash: true -> trailingSlash: false in next.config.js seems to fix the issue on my starter-derived project, maybe one of you could make that change on this PR and see if that fixes the E2E tests?

[jackbravo]

It worked @lukeramsden ! 🎉

@benjie this seems ready now.

[benjie]

Awesome; merged into #222

[benjie]

Sorry for the delay; took a long time to track down a bug that turned out to be next build not working quite right in NODE_ENV=test