Hello Dimitris,
Based on your first message it seems to me that your customer would like to limit the authentication of certain group of users on specific PCs (for example shared PCs/kiosk PCs). Using the Risk-based authentication solution of our SAP Single Sign-On product it is possible to implement such complicated security requirements, like for example the one that you have from your customer now.
Here you will be able to find my blog about the solution:
Risk-Based Authentication for Your Critical Business Processes
Stronger security for your business data at risk
Also if you are interested to find more info about this solution and the SSO technologies and the two-factor authentication supported by our product, I will be glad to do a presentation and a demo to you and your team and to discuss in details how out features could help you to implement the requirements of your customer.
If you are interested just send me a message on donka.dimitrova at sap.com.
Regards,
Donka Dimitrova