Too busy to man the gates yourself? Use a bouncer like Auth0.
In one of the projects Expero worked on several years ago, the client chose to build their own custom authentication solution. For three weeks, one developer’s status at the scrum every morning was “security.” It took that competent developer several weeks to get a very basic custom solution in place. Additionally, that solution didn’t even have integration with other identity providers or any other bells and whistles! You can easily double that estimate if you want even a few providers and a user interface that doesn’t look drab.