Hello Gaurav,
if you are using entity based authorizations,you should have access to authorization object
GRFN_API with activity as change, entity as ORGUNIT, sub entity as * and data part as ROLES or ROLES_PC.
ROLES is used for role assignment to shared entities such as controls
ROLES_PC is used for role assignment to PC entities such as sub process
You can check component of entities in table GRFNENTITY
i hope this will resolve your issue.
Regards
Baithi