INT 2F - License Service API - REQUEST LICENSE
        AX = 7001h
        CX = license server index (0000h to 001Fh)
        DS:DX -> SLSREQUEST structure (see below)
Return: AX = status
            0000h success
            else  provider error code
        ES:BX = provider specific handle for the license context
SeeAlso: AX=7002h,AX=7004h,AX=7005h

Format of SLSREQUEST structure:
Offset  Size    Description
 00h    DWORD   (return) status code
 04h    DWORD   (return) handle identifying context
 08h    DWORD   (call) address of Publisher string
 0Ch    DWORD   (call) address of Product string
 10h    DWORD   (call) address of Version string
 14h    DWORD   units required
 18h    DWORD   address of comment string
 1Ch    DWORD   address of SLSCHALLENGE structure (see below)

Format of SLSCHALLENGE structure:
Offset  Size    Description
 00h    DWORD   algorithm (currently always 1)
 04h    DWORD   secret to be challenged (1-255)
 08h    DWORD   size of challenge in bytes (1-255)
 0Ch  N BYTEs   challenge data

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