(core) support access control on columns

Summary: Adds a granular access clause for columns. Permissions can be specified for a set of columns within a table. Permissions accumulate over clauses, in a way that is intended as a placeholder pending final design.

Test Plan: Added tests. Tested manually that updates to private columns are not sent to people who don't have access to them. There are a lot of extra tests needed and TODOs to be paid down after this experimental phase.

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2651

app/common/GranularAccessClause.ts

@@ -10,6 +10,7 @@ export type GranularAccessClause =
   GranularAccessDocClause |
   GranularAccessTableClause |
   GranularAccessRowClause |
+  GranularAccessColumnClause |
   GranularAccessCharacteristicsClause;
 
 /**
@@ -41,6 +42,18 @@ export interface GranularAccessRowClause {
   scope?: MatchSpec;
 }
 
+/**
+ * A clause to control access to columns within a specific table.
+ */
+export interface GranularAccessColumnClause {
+  kind: 'column';
+  tableId: string;
+  colIds: string[];
+  match: MatchSpec;
+  onMatch?: AccessPermissionDelta;  // permissions to apply if match succeeds
+  onFail?: AccessPermissionDelta;   // permissions to apply if match fails
+}
+
 /**
  * A clause to make more information about the user/request available for access
  * control decisions.
@@ -59,6 +72,17 @@ export interface GranularAccessCharacteristicsClause {
   lookupColId: string; // column in which to look it up
 }
 
+/**
+ * A sketch of permissions, intended as a placeholder.
+ */
+export type AccessPermission = 'read' | 'update' | 'create' | 'delete';
+export type AccessPermissions = 'all' | AccessPermission[];
+export interface AccessPermissionDelta {
+  allow?: AccessPermissions;      // permit the named operations
+  allowOnly?: AccessPermissions;  // permit the named operations, and forbid others
+  forbid?: AccessPermissions;     // forbid the named operations
+}
+
 // Type for expressing matches.
 export type MatchSpec = ConstMatchSpec | TruthyMatchSpec | PairMatchSpec | NotMatchSpec;