Credential provider usage scenario: CPUS_UNLOCK_WORKSTATION removed from Windows 10

I am currently investigating the same issue and may have a work around until Microsoft can update the documentation.

Although I still receive a CPUS_LOGON, we are still inside the same session as the locked user. By using the function WTSQuerySessionInformationW, you can verify that there is currently a user logged in to the current session. From there, you can proceed as if you were in a CPUS_UNLOCK_WORKSTATION usage scenario.

UPDATE (1/18/2016): It seems Microsoft has finally updated their documentation on this issue. See the excerpt below from the CREDENTIAL_PROVIDER_USAGE_SCENARIO documentation:

Starting in Windows 10, the CPUS_LOGON and CPUS_UNLOCK_WORKSTATION user scenarios have been combined. This enables the system to support multiple users logging into a machine without creating and switching sessions unnecessarily. Any user on the machine can log into it once it has been locked without needing to back out of a current session and create a new one. Because of this, CPUS_LOGON can be used both for logging onto a system or when a workstation is unlocked. However, CPUS_LOGON cannot be used in all cases. Because of policy restrictions imposed by various systems, sometimes it is necessary for the user scenario to be CPUS_UNLOCK_WORKSTATION. Your credential provider should be robust enough to create the appropriate credential structure based on the scenario given to it. Windows will request the appropriate user scenario based on the situation. Some of the factors that impact whether or not a CPUS_UNLOCK_WORKSTATION scenario must be used include the following. Note that this is just a subset of possibilities.

• The operating system of the device.
• Whether this is a console or remote session.
• Group policies such as hiding entry points for fast user switching, or interactive logon that does not display the user's last name.

Credential providers that need to enumerate the currently user logged into the system as the default tile can keep track of the current user or leverage APIs such as WTSQuerySessionInformation to obtain that information