[RFC] disable query/subscription root fields

PR-URL: hasura/graphql-engine-mono#4449
GitOrigin-RevId: f7f4e60250b4c7375a973d0e5770ac134217767a

Author: codingkarthik

rfcs/disable-query-and-subscription-root-fields.md

@@ -0,0 +1,81 @@
+original issue: https://github.com/hasura/graphql-engine/pull/4110
+
+## Allow disabling query root fields
+
+Currently when a select permission is defined for a role on a table, we
+automatically generate 3 fields for the table (`<table>`, `<table_by_pk>`,
+`<table_aggregate>`) in `query_root` and likewise in `subscription_root`.  This
+should be customisable to allow some of the patterns as discussed below.
+
+### Motivation
+
+#### 1. Allow selecting data only through relationships (issues: [207](https://github.com/hasura/graphql-engine/issues/207), [696](https://github.com/hasura/graphql-engine/issues/696), [3742](https://github.com/hasura/graphql-engine/issues/3742)).
+
+Let's say you have a slack like application with the following schema:
+
+| table | columns | relationships |
+|-------|---------|---------------|
+| workspace | id, name | members(array, to workspace_membership) |
+| workspace_membership | workspace_id, user_id |
+| channel | id, name, workspace_id | workspace(object, to workspace) |
+| message | id, content, user_id, channel_id | channel(object, to channel) |
+
+The permissions for a `user` role would be something along these lines:
+
+| table | permissions |
+|-------|-------------|
+| workspace | `{"members": {"user_id": "x-hasura-user-id"}}` |
+| channel | `{"workspace": {"members": {"user_id": "x-hasura-user-id"}}}` |
+| message | `{"channel": {"workspace": {"members": {"user_id": "x-hasura-user-id"}}}}` |
+
+Now let's say we would like to introduce a new table called `message_reaction`
+which has columns (message_id, reaciton_name, user_id). The permission on
+`message_reaction` table would be as follows:
+
+```json
+{"message": {"channel": {"workspace": {"members": {"user_id": "x-hasura-user-id"}}}}}
+```
+
+As we go down the chain, our permissions gets more and more nested, refering to
+the permissions of the parent tables and beyond a point can get quite
+cumbersome. Let's say in our application we **never** need to access
+`message_reactions` table directly and is always accessed through `reactions`
+relationship on `message` table. Can the permission be simplified?
+
+Yes! *If we can disable all of the `message_reaction` table's top level
+fields*, the select filter on `message_reactions` table can be simplified to
+`{}` and as `message` table has the correct permissions, the relationship
+`reactions` is restricted to what can be accessed through `message` table.
+
+The pattern where certain data can only be accessible through relationships
+seems to be known as 'Aggregate' pattern under [Domain-Driven
+Design](https://martinfowler.com/bliki/DDD_Aggregate.html).
+
+#### 2. As an additional access control mechanism
+
+Let's say you want to allow a client to fetch data from a table only if the
+client knows the primary key of a row in that table. In this case regardless of
+the permission on the table, only `<table>_by_pk` should be exposed in
+`query_root`.
+
+## Allow disabling subscription fields
+
+Currently we do not provide a fine grained control on subscriptions that are exposed - if a select permission is defined on a table, the live queries on that table are exposed through `subscription_root`. (Note: the discussion of `query_root` customisability also applies to `subscription_root`).
+
+### Proposed solution
+
+Introduce optional `query_root_fields` and `subscription_root_fields` in select permission which takes a list of `field`s that should be exposed in `query_root` (where `field` is one of `select`/`select_by_pk`/`select_aggregate`) and `subscription_root` (`query_root` fields + `select_stream`) respectively. When these fields are absent, all the values are enabled. The current behaviour is for backwards compatibility.
+Note: The Relay field `<table>_connection` will be enabled if `select` is given in `query_root_fields` else it will be disabled.
+
+### Metadata API behaviour
+
+For incremental metadata API (`create_select_permission`), throw validation error when:
+    a. A role doesn't have access to the primary key column(s) and `select_by_pk` is added.
+    b. When `select_stream` is added when streaming subscriptions is not enabled in the graphql-engine.
+    c. When `select_aggregate` is added without `allow_aggregations` set to `true`.
+
+For `replace_metadata` API, throw validation error in the above cases when `allow_inconsistent_metadata: false` else mark invalid permissions as inconsistent objects.
+
+### Future work
+
+1. Extend this feature for mutations and remote schemas.