Added role permissions for exporting content

app/Http/Middleware/CheckUserHasPermission.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace BookStack\Http\Middleware;
+
+use Closure;
+use Illuminate\Http\Request;
+
+class CheckUserHasPermission
+{
+    /**
+     * Handle an incoming request.
+     *
+     * @param \Illuminate\Http\Request $request
+     * @param \Closure                 $next
+     * @param                          $permission
+     *
+     * @return mixed
+     */
+    public function handle($request, Closure $next, $permission)
+    {
+        if (!user()->can($permission)) {
+            return $this->errorResponse($request);
+        }
+
+        return $next($request);
+    }
+
+
+    protected function errorResponse(Request $request)
+    {
+        if ($request->wantsJson()) {
+            return response()->json(['error' => trans('errors.permissionJson')], 403);
+        }
+
+        session()->flash('error', trans('errors.permission'));
+        return redirect('/');
+    }
+}