chore: reorder prebuilt workspace authorization logic (#18506)

## Description

Follow-up from PR https://github.com/coder/coder/pull/18333
Related with:
https://github.com/coder/coder/pull/18333#discussion_r2159300881

This changes the authorization logic to first try the normal workspace
authorization check, and only if the resource is a prebuilt workspace,
fall back to the prebuilt workspace authorization check. Since prebuilt
workspaces are a subset of workspaces, the normal workspace check is
more likely to succeed. This is a small optimization to reduce
unnecessary prebuilt authorization calls.

coderd/database/dbauthz/dbauthz.go

@@ -151,26 +151,28 @@ func (q *querier) authorizeContext(ctx context.Context, action policy.Action, ob
 
 // authorizePrebuiltWorkspace handles authorization for workspace resource types.
 // prebuilt_workspaces are a subset of workspaces, currently limited to
-// supporting delete operations. Therefore, if the action is delete or
-// update and the workspace is a prebuild, a prebuilt-specific authorization
-// is attempted first. If that fails, it falls back to normal workspace
-// authorization.
+// supporting delete operations. This function first attempts normal workspace
+// authorization. If that fails, the action is delete or update and the workspace
+// is a prebuild, a prebuilt-specific authorization is attempted.
 // Note: Delete operations of workspaces requires both update and delete
 // permissions.
 func (q *querier) authorizePrebuiltWorkspace(ctx context.Context, action policy.Action, workspace database.Workspace) error {
-	var prebuiltErr error
-	// Special handling for prebuilt_workspace deletion authorization check
+	// Try default workspace authorization first
+	var workspaceErr error
+	if workspaceErr = q.authorizeContext(ctx, action, workspace); workspaceErr == nil {
+		return nil
+	}
+
+	// Special handling for prebuilt workspace deletion
 	if (action == policy.ActionUpdate || action == policy.ActionDelete) && workspace.IsPrebuild() {
-		// Try prebuilt-specific authorization first
+		var prebuiltErr error
 		if prebuiltErr = q.authorizeContext(ctx, action, workspace.AsPrebuild()); prebuiltErr == nil {
 			return nil
 		}
+		return xerrors.Errorf("authorize context failed for workspace (%v) and prebuilt (%w)", workspaceErr, prebuiltErr)
 	}
-	// Fallback to normal workspace authorization check
-	if err := q.authorizeContext(ctx, action, workspace); err != nil {
-		return xerrors.Errorf("authorize context: %w", errors.Join(prebuiltErr, err))
-	}
-	return nil
+
+	return xerrors.Errorf("authorize context: %w", workspaceErr)
 }
 
 type authContextKey struct{}

coderd/database/dbauthz/dbauthz_test.go

@@ -5650,7 +5650,17 @@ func (s *MethodTestSuite) TestAuthorizePrebuiltWorkspace() {
 			Reason:            database.BuildReasonInitiator,
 			TemplateVersionID: tv.ID,
 			JobID:             pj.ID,
-		}).Asserts(w.AsPrebuild(), policy.ActionDelete)
+		}).
+			// Simulate a fallback authorization flow:
+			// - First, the default workspace authorization fails (simulated by returning an error).
+			// - Then, authorization is retried using the prebuilt workspace object, which succeeds.
+			// The test asserts that both authorization attempts occur in the correct order.
+			WithSuccessAuthorizer(func(ctx context.Context, subject rbac.Subject, action policy.Action, obj rbac.Object) error {
+				if obj.Type == rbac.ResourceWorkspace.Type {
+					return xerrors.Errorf("not authorized for workspace type")
+				}
+				return nil
+			}).Asserts(w, policy.ActionDelete, w.AsPrebuild(), policy.ActionDelete)
 	}))
 	s.Run("PrebuildUpdate/InsertWorkspaceBuildParameters", s.Subtest(func(db database.Store, check *expects) {
 		u := dbgen.User(s.T(), db, database.User{})
@@ -5679,6 +5689,16 @@ func (s *MethodTestSuite) TestAuthorizePrebuiltWorkspace() {
 		})
 		check.Args(database.InsertWorkspaceBuildParametersParams{
 			WorkspaceBuildID: wb.ID,
-		}).Asserts(w.AsPrebuild(), policy.ActionUpdate)
+		}).
+			// Simulate a fallback authorization flow:
+			// - First, the default workspace authorization fails (simulated by returning an error).
+			// - Then, authorization is retried using the prebuilt workspace object, which succeeds.
+			// The test asserts that both authorization attempts occur in the correct order.
+			WithSuccessAuthorizer(func(ctx context.Context, subject rbac.Subject, action policy.Action, obj rbac.Object) error {
+				if obj.Type == rbac.ResourceWorkspace.Type {
+					return xerrors.Errorf("not authorized for workspace type")
+				}
+				return nil
+			}).Asserts(w, policy.ActionUpdate, w.AsPrebuild(), policy.ActionUpdate)
 	}))
 }

coderd/database/modelmethods.go

@@ -199,6 +199,13 @@ func (gm GroupMember) RBACObject() rbac.Object {
 	return rbac.ResourceGroupMember.WithID(gm.UserID).InOrg(gm.OrganizationID).WithOwner(gm.UserID.String())
 }
 
+// PrebuiltWorkspaceResource defines the interface for types that can be identified as prebuilt workspaces
+// and converted to their corresponding prebuilt workspace RBAC object.
+type PrebuiltWorkspaceResource interface {
+	IsPrebuild() bool
+	AsPrebuild() rbac.Object
+}
+
 // WorkspaceTable converts a Workspace to it's reduced version.
 // A more generalized solution is to use json marshaling to
 // consistently keep these two structs in sync.