“When need becomes necessity” - The single digital gateway regulation and the once-only principle from a European point of viewSchmidt, Carsten; Krimmer, Robert Johannes; Lampoltshammer, Thomas J.Open Identity Summit 2021: Fachtagung vom 01.-02. Juni 2021 Copenhagen2021 / p. 223-228 https://dl.gi.de/server/api/core/bitstreams/ec03538d-b376-4537-bc0f-aab2936c74f8/content Conference Proceedings at Scopus Article at Scopus