handlers: permisison check for all pages + retrieve user-specific permissions for pages (if any)

handlers/handler.h

@@ -18,6 +18,8 @@ class Handler
 	Session *userSession;
 	UrlProvider *urlProvider;
 
+	// TODO: may not to find a better place for this method
+	Permissions effectivePermissions(std::string page);
 	QueryOption queryOption(const Request &r) const;
 
   public:
@@ -29,7 +31,21 @@ class Handler
 		this->urlProvider = &provider;
 		this->cache = &cache;
 	}
-	virtual Response handle(const Request &r) = 0;
+
+	virtual Response handle(const Request &r);
+	virtual Response handleRequest(const Request &r)
+	{
+		return this->errorResponse("Invalid action", "This action is not implemented yet");
+	}
+
+	virtual bool canAccess(const Permissions &perms)
+	{
+		return false;
+	}
+	virtual std::string accessErrorMessage()
+	{
+		return "No permission for this action";
+	}
 	void setGeneralVars(TemplatePage &page);
 	virtual ~Handler()
 	{