Authorization key for the user profile

In SAP, there is a provision where we can create the authorization key and assign this key to the various user statuses in the user status profile.

The application is that when the user status is changed from one to other and if to the user status, the authorisation key is assigned then the authorised person should be only able to change the status.

But my query is that i have not come across any customization where a SAP user can be assigned to the auth. key so that he can only change the user status.

Can anybody let me know that whatever i understood, is it correct? And if yes, let me know where to assign the user to the authorisation key?

Thanks