Backport documentation fixes

[thomasdziedzic-pd]

#33170

[rails-bot]

Thanks for the pull request, and welcome! The Rails team is excited to review your changes, and you should hear from @schneems (or someone else) soon.

If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes.

This repository is being automatically checked for code quality issues using Code Climate. You can see results for this analysis in the PR status below. Newly introduced issues should be fixed before a Pull Request is considered ready to review.

Please see the contribution instructions for more information.

[rails-bot]

Warning

• Pull requests are usually filed against the master branch for this repo, but this one is against 5-2-stable. Please double check that you specified the right target!

[utilum]

The original motivation for #33170 is addressed by this patch. These config vars are in use in 5.2

[utilum]

#33172 was also merged into 5-2-stable. So only the second of the two commits here is still needed.

[thomasdziedzic-pd]

Updated the commits to reflect the backport being added.

[bogdanvlviv]

Yes it should be backported to 5-2-stable since
action_dispatch.use_authenticated_cookie_encryption is true by default https://github.com/rails/rails/blob/5-2-stable/railties/lib/rails/application/configuration.rb#L102

Related to c8a22bb.

Thank you for the PR!