How to manage user Id/password for Account in customer Application

If we used Web access view under contact screen to maintain user id/password and grant responsibility for a eService user, how can we can distinguish this user whether he is a particular customer or a Account administrator.

As a particular customer, he can update information of himself, for example, address, phone number etc. He can’t see any other view.
As an Account administrator, he can only see the account he belongs to and he can update the account’s information like address, major description, etc.
We know that we can use responsibility to control the view which the user can see. However, we would like to know how to manage the ID and password for Account administrator.