Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _WINSTA_H

// Retrieves the current shadow state of a session.
typedef struct _WINSTATIONSHADOW
    SHADOWSTATECLASS ShadowState; // Specifies the current state of shadowing.
    SHADOWCLASS ShadowClass; // Specifies the type of shadowing.
    ULONG SessionId; // Specifies the session ID of the session.
    ULONG ProtocolType; // Specifies the type of protocol on the session. Can be one of PROTOCOL_* values.


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This type is documented in the [MS-TSTS] specification.