If enabled then only those sessions that are configured for one-way CHAP may be established. If disabled then sessions that are configured for one-way CHAP or sessions not configured for one-way CHAP may be established. Note that if the “Do not allow sessions without mutual CHAP” setting is enabled then that setting overrides this one.
HKEY_LOCAL_MACHINE -> Software -> Policies -> Microsoft -> Windows -> iSCSI # RequireOneWayCHAP
System -> iSCSI -> iSCSI Security