I have seen some cases recently with requests to force users to sign-in before accessing any content on their Dynamics 365 Portal.  

Setting the LoginButtonAuthenticationType is needed, but the users will not be authenticated without selecting sign in without step 4 below.  Steps 1 and 3 will need to be changed based on your auth provider. Also remember this only redirects the users to the auth provider you specify in step 2, users may still need to enter credentials based on how the provider is configured.  

 

Steps to configure SSO using Azure AD as the auth provider 

1.  In the portal when signing in select the Azure AD button and copy the URL it redirects to as we will need the first GUID in this URL in step 3 ex. https://login.microsoftonline.com/a34b6aec-7b52-6fd5-q28b-889d48def358/oauth2/authorize?client_id...

2. In your Dynamics 365 organization open the Authentication/Registration/LoginButtonAuthenticationType record in the portal - site settings area.  If this has not created it will need to be done now.

3. The value here will be https://login.windows.net/a34b6aec-7b52-6fd5-q28b-889d48def358/ where the GUID is the same as the one from the login button above.

4. Now in your organization open the Web Page Access Control Rules and create a new one.

Settings:

                Name:  Can be anything you choose

                Website:  Use the lookup to find your site

                Web Page:  Use the lookup to find Home 

                Right:  Restrict Read

 

Under the Web Roles section:

                Add Authenticated users

5. After the settings above are saved the authentication should work as expected after the cache is invalidated.