A company wants to implement the Power Apps portal. It expects that authenticated and unauthenticated users visit the portal. The company asks you to design its portal authentication. 
Please select all correct statements about portal authentication.

Answer options:

A.Portal users can have several logins with the same email address
B.Each authenticated portal user has a contact record in the Dataverse database
C.If open registration is enabled, users must provide an invitation code for portal sign-up
D.Each registered portal users must have an assigned web role
E.Portal admin can set a default identity provider on the Authentication Settings panel
F.Facebook authentication provider uses OpenId protocol

Correct Answers: B, D and E 
By default, anybody can use the Power Apps portal as an unauthenticated user. However, if users want to register for the portal login, there are two methods: Local authentication — creates a local identity with a username and password stored in a Dataverse database internally.
External authentication — uses credentials of the third-party identity providers, like OAuth2 (Microsoft, Twitter, Facebook, Google, etc.), OpenID (Azure AD, Azure AD B2C), and WS-Federation and SAML 2.0 (AD on-premises).
Option B is correct because a portal creates a contact record in the Dataverse database for each authenticated user.
Option D is correct because a portal assigns a web role to each authenticated user. The role defines a user`s access to portal resources.
Option E is correct because a portal administrator can enable/disable Identity providers and set them as default on the portal`s Authentication Settings panel. On the same panel, you can add a new provider.
Option A is incorrect because portal users must have a unique email address for each portal account. Users cannot reuse an email address.
Option C is incorrect because users do not require an invitation code for portal sign-up if open registration is enabled.
Option F is incorrect because the Facebook provider uses OAuth2 but not OpenID protocol. 
For more information about Power Apps portal authentication, please visit the below URLs: 

https://docs.microsoft.com/en-us/learn/modules/introduction-power-apps-portals/06-overview-portals-security
https://docs.microsoft.com/en-us/learn/modules/power-apps-architecture/7-portals
https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/use-simplified-authentication-configuration
https://docs.microsoft.com/en-us/powerapps/maker/portals/configure/configure-portal-authentication