- The current architecture is inherently insecure, because you can
construct the 'secret' cookie value with values that are available in
the database. Thus provides zero protection when a database is
dumped/leaked.
- This patch implements a new architecture that's inspired from: [Paragonie Initiative](https://paragonie.com/blog/2015/04/secure-authentication-php-with-long-term-persistence#secure-remember-me-cookies).
- Integration testing is added to ensure the new mechanism works.
- Removes a setting, because it's not used anymore.
(cherry picked from commit eff097448b)
[GITEA] rework long-term authentication (squash) add migration
Reminder: the migration is run via integration tests as explained
in the commit "[DB] run all Forgejo migrations in integration tests"
(cherry picked from commit 4accf7443c)
(cherry picked from commit 99d06e344ebc3b50bafb2ac4473dd95f057d1ddc)
d8bc98a8f0