You need to set up authentication for the Power Apps portal based only on the OAuth2 protocol. 
Please select all identity providers that you should enable for your portal.

Answer options:

A.Local sign in
B.Twitter
C.Azure AD
D.Microsoft
E.Azure AD B2C
F.Google

Correct Answers: B, D and F 
By default, anybody can use the Power Apps portal as an unauthenticated user. If users want to register at the portal, 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.
Power Apps portal divides external providers by the authentication protocol: 

Portal administrators can enable/disable Identity providers and set them as default on the portal’s Authentication Settings panel. On the same panel, we can add or modify a provider. 
For each authenticated user, a portal creates a contact record in the Dataverse database. It also assigns a web role. The role defines a user`s access to portal resources. 
All other options are incorrect. 
For more information about Power Apps portal authentication, please visit the below URLs: 

https://docs.microsoft.com/en-us/learn/modules/authentication-user-management/5-authentication-providers
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