RegistryUI can use a Microsoft Login Provider so users can log into RegistryUI using their Microsoft account. Before users can log in, the site administrator must add the user using Registry > Users & Groups and send an invitation email to the user with an invitation code. This invitation code is required when logging in using a Microsoft account the very first time.
In order to enable the Microsoft Login Provider at Admin > Login Providers, External Login tab, a Microsoft Application ID and Microsoft Client Secret must be obtained. This can be done on Microsoft's site at https://portal.azure.com/#blade/Microsoft_AAD_RegisteredApps/ApplicationsListBlade.
Select New registration and enter a name.
Select an option for Supported account types.
Enter the following as Redirect URIs:
https://yourregistry.yourcompany.com/signin-microsoft or http://yourregistry.yourcompany.com/signin-microsoft (not recommended)
Then click the "Register" button.
Then click Certificates & secrets (along the left menu bar) followed by the "New client secret" button.
Enter a Description for the new client secret, select an expiration and click Add.