List of missing APIs

Let's collect a list of information we don't expose yet, but might be helpful to build a partially decoupled admin UI:

1. A list of all permissions #2947605: Add a user permissions resourceLink
2. A list of modules (enabled and disabled ones): Link
3. Changing passwords: #2904451: Allow to change password through RPC endpoints through the reset password workflow
4. Menu links: #2732283: Menus: ability to retrieve all menu links for a given menu, regardless of whether a menu link is defined in content/config/code / Menu Tree: https://github.com/jsdrupal/drupal-admin-ui/pull/23
5. Code-based, not config-based provisioning of REST resources: #2822201: Allow contrib modules to deploy REST resources by creating routes, removing the need for config entities in that special case
6. Conveying which fields can be edited: #2665602: Implement an API for REST clients to know which fields are editable
7. #2919182: Web service to download private:// files
8. #2771353: Support "auto-create" entity references by value (instead of by ID/UUID), just like tags are auto-created in the content creation UI
9. #1869338: Support ETag + If-Match for PATCH requests to prevent concurrent updates
10. #1916302: RFC 7807: "Problem Details for HTTP APIs"— serve REST error responses as application/problem+json
11. #2947759: Simple configuration REST support
12. State API - This would let you put a site in maintenance mode
13. UserData - This is what stores whether the user contact form is enabled or not
14. Cache rebuild