Hi @Anonymous ,
Again, as @OliverRodrigues mentioned this is really tricky to answer. Adding few more points
1. Two-factor authentication is available but it is not supported by portals yet. You can do some out-of-the-box features.
2. Multi-Factor authentication is only available if you configure Active Directory Federated Services (AD FS) with Azure MFA.
3. Passwordless is not yet available. But I believe in the future this will be available.
4. If you have plans to build a companion app to support powerapps portal, probably authentication and cross-site forgery should be taken into consideration. Ref: about companion app: https://www.engineeredcode.com/blog/dynamics-365-portal-custom-server-side-code-with-a-companion-app
Hope it helps.
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