A new control function is defined for the control plane of a 5G mobile network to enable the operator's mobile user, who is using a premium network slice, to access application services on the public Internet, by operator sign-on only when accessing the application on said slice. This unique single sign-on capability allows the user to bypass the service authentication after operator authenticates the mobile device by the user session establishment procedure. The new function registers a plurality of service applications, which sign-up for single sign-on capability. It also coordinates the mapping and storage of credentials of the user across the mobile operator's service and the service provider's application for each of said plurality of service applications, and transfers user credentials to the application so that the user's sign-in step is bypassed.