SE_X.H

The public symbol file NTKRPAMP.PDB for the original release of Windows 10 tells that the kernel is built with the SE_X.H header at

d:\th\minkernel\ntos\inc

and draws from it the following type definitions:

Line Number	Type	WDM.H	NTOSP.H
41	enum _SECURITY_OPERATION_CODE	25889	39084
88	struct _SECURITY_SUBJECT_CONTEXT	25904	39099
112	struct _INITIAL_PRIVILEGE_SET	25926	39121
126	struct _ACCESS_STATE	25940	39135
139	unnamed union for Privileges in _ACCESS_STATE	25953	39148
159	struct _AUX_ACCESS_DATA		39166

The header SE_X.H is not known in any Device Driver Kit (DDK) or Windows Driver Kit (WDK).