In Dynamics 365 Portal there is a Site Setting records which defines the registration behaviour if portal. By default the options to login or register with the portal are as follows:
- Sign In
- Redeem Invitation
- Sign in with an external account
However we can disable some options from the above if we don't need them
1. Disable local login:
Go to Authentication/Registration/LocalLoginEnabled and set its Value to false.
Now this will hide the Sign in with Local Account option as shown in the following screenshot.
2. Disable Registration option:
Go to Authentication/Registration/Enabled and set its Value to false
This will hide the Registration tabs from the sign in page as shown in the following screenshot.
3. Disable both Local Login and Registration to false
Now as we have set both the Site Settings to false so as a result the only option available to the user for Signing in to the portal is Azure AD.