Sharepoint - Add permission to all authenticated users

You can provide permissions to following groups :

1. All Authenticated Users: All user accounts which can be recognized by SharePoint Online, both for internal and external.

2. All Users (Windows) : User accounts from Federated domains.

3. All Users (membership): All user accounts from Office 365 Online Services.

Everyone was what worked for me

EDIT Everyone is a default group that contains all authenticated and guest users that can connect to your network.