Microsoft Authenticator is currently being tested internally and therefor still has no download option.
Here is what the App description says:
“The first step towards a world without passwords! After a quick Bluetooth sync, use this app to unlock your Windows 10 computer at work. Just open the app and tap on a nearby computer.
Note: This app is still in beta. Future versions will include support for Microsoft account, a sign in solution for browsers and VPN. one-time passcode generation, and MFA approval through notifications.”
As we can see from the specs of Microsoft Authenticator, the app will have access to webcam, bluetooth and the internet connection.
It will be able to add an AAD Account which stands for Azure Active Directory, Microsoft's multi-tenant cloud based directory and identity management service.
Azure Active Directory includes a full suite of identity management capabilities including multi-factor authentication, device registration, self-service password management, self-service group management, privileged account management, role based access control, application usage monitoring, rich auditing and security monitoring and alerting.
Using the Azure Active Directory service, Microsoft Authenticator will be able to unlock Windows PCs remotely via unattended authentication. You can find some more technical details about this technology in this great post from Tom Hollander: Unattended authentication to Azure Management APIs with Azure Active Directory.