Permissions configurations (or edit space/page restrictions) logging should be implemented based on the doeditspacepermissions.action and pacakage com.atlassian.confluence.security.actions.EditSpacePermissionsAction. This option should be made available for monitoring and auditing purposes.

Update: The Space Permission changes are now tracked by the Audit Log of Confluence. Still, this feature remains open as we don't have means to track Page Restriction changes.