Introduce polymorphic resource owner

[nbulaj]

Adds long-awaited ability to set polymorphic Resource Owner for Access Token & Grant (and not just it's ID).

Fixes #1069
Fixes #651
Fixes #456
Fixes #233

TODO

• Add configuration option to enable polymorphic resource owner
• Refactor existing code base to use resource owner instance and no just it's ID
  • Make it backward compatible as much as possible
• Add generator for new migration with required columns
• Document changes, add to initializer
• Cover it all with specs

How to use it

Enable configuration option:

Doorkeeper.configure do
  orm :active_record

  use_polymorphic_resource_owner
end

Generate migration to add polymorphic columns to tables:

$ bundle exec rails g doorkeeper:enable_polymorphic_resource_owner

If you previously set foreign key for :resource_owner_id column - you need to drop it as now it would be a polymorphic association. Add it to the migration generated above.

Run the migration:

$ bundle exec rails db:migrate

Use it! 🤠

⚠️ ⚠️ [ATTENTION]: If you enabled this option on existing project - you need to manually set polymorphic type column with the class of the Resource Owner. Otherwise your existing users/clients could face issues and spam you logs with errors.

⚠️ ⚠️ [ATTENTION]: Also this feature could be a breaking change for those users that patched Doorkeeper internals, specially models. You need to fix your patches to user resource_owner instance instead of it's ID (like it was before).

Known projects affected

• GitLab (https://gitlab.com/gitlab-org/gitlab-foss/blob/master/config/initializers/doorkeeper.rb#L129)
• Doorkeeper ORM extensions

[jturkel]

It's so awesome to see this supported out of the box! Are there any plans to support restricting oauth applications by resource owner type e.g. one set of oauth applications for "users" and a disjoint set for "operators"? I guess #1354 would make this possible with an appropriately configured block.

[nbulaj]

OK, I'll try to add some specs later, need to think more about how to reload mixins and models that depends on Doorkeeper config (and polymcorphic resource owner option).