[BRC-3414] Add PG hook for oauth token permission check

We need an additional hook to perform backup permission-checking after
the native PG check fails.

Author: Eric Pei

src/backend/executor/execMain.c

@@ -70,6 +70,9 @@ ExecutorEnd_hook_type ExecutorEnd_hook = NULL;
 /* Hook for plugin to get control in ExecCheckPermissions() */
 ExecutorCheckPerms_hook_type ExecutorCheckPerms_hook = NULL;
 
+/* Backup hook to check for rte permissions after native permissions check fails */
+ExecutorUnityCatalogCheckPerms_hook_type ExecutorUnityCatalogCheckPerms_hook = NULL;
+
 /* decls for local routines only used within this module */
 static void InitPlan(QueryDesc *queryDesc, int eflags);
 static void CheckValidRowMarkRel(Relation rel, RowMarkType markType);
@@ -613,6 +616,18 @@ ExecCheckPermissions(List *rangeTable, List *rteperminfos,
 
 		Assert(OidIsValid(perminfo->relid));
 		result = ExecCheckOneRelPerms(perminfo);
+
+		// BEGIN HADRON
+		// If we don't have the necessary native Postgres permission,
+		// check if our Databricks OAuth token grants us permission.
+		if (!result)
+		{
+			if (ExecutorUnityCatalogCheckPerms_hook)
+				result = (*ExecutorUnityCatalogCheckPerms_hook) (perminfo);
+
+		}
+		// END HADRON
+
 		if (!result)
 		{
 			if (ereport_on_violation)

src/include/executor/executor.h

@@ -96,6 +96,10 @@ typedef bool (*ExecutorCheckPerms_hook_type) (List *rangeTable,
 											  bool ereport_on_violation);
 extern PGDLLIMPORT ExecutorCheckPerms_hook_type ExecutorCheckPerms_hook;
 
+/* Backup hook to check for Unity Catalog permissions after native permissions check fails */
+typedef bool (*ExecutorUnityCatalogCheckPerms_hook_type) (RTEPermissionInfo *perminfo);
+extern PGDLLIMPORT ExecutorUnityCatalogCheckPerms_hook_type ExecutorUnityCatalogCheckPerms_hook;
+
 
 /*
  * prototypes from functions in execAmi.c