Add API access check to Graphql

Check if user can access API on GraphqlController

app/controllers/graphql_controller.rb

@@ -12,6 +12,7 @@ class GraphqlController < ApplicationController
   protect_from_forgery with: :null_session, only: :execute
 
   before_action :check_graphql_feature_flag!
+  before_action :authorize_access_api!
   before_action(only: [:execute]) { authenticate_sessionless_user!(:api) }
 
   def execute
@@ -37,6 +38,10 @@ class GraphqlController < ApplicationController
 
   private
 
+  def authorize_access_api!
+    access_denied!("API not accessible for user.") unless can?(current_user, :access_api)
+  end
+
   # Overridden from the ApplicationController to make the response look like
   # a GraphQL response. That is nicely picked up in Graphiql.
   def render_404

changelogs/unreleased/issue_58547.yml

+---
+title: Add API access check to Graphql
+merge_request: 26570
+author:
+type: other

spec/controllers/graphql_controller_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe GraphqlController do
+  before do
+    stub_feature_flags(graphql: true)
+  end
+
+  describe 'POST #execute' do
+    context 'when user is logged in' do
+      let(:user) { create(:user) }
+
+      before do
+        sign_in(user)
+      end
+
+      it 'returns 200 when user can access API' do
+        post :execute
+
+        expect(response).to have_gitlab_http_status(200)
+      end
+
+      it 'returns access denied template when user cannot access API' do
+        # User cannot access API in a couple of cases
+        # * When user is internal(like ghost users)
+        # * When user is blocked
+        expect(Ability).to receive(:allowed?).with(user, :access_api, :global).and_return(false)
+
+        post :execute
+
+        expect(response.status).to eq(403)
+        expect(response).to render_template('errors/access_denied')
+      end
+    end
+
+    context 'when user is not logged in' do
+      it 'returns 200' do
+        post :execute
+
+        expect(response).to have_gitlab_http_status(200)
+      end
+    end
+  end
+end