A system comprising an IMS network (104), an adapter module (106), an identity provider (108) and an application (110) is described. The adapter module (106) is within an IMS trust domain. The application (110) is within the trust domain of the identity provider. A user of the system can access the application (110) via the IMS network (104), regardless of whether the application is within the IMS trust domain, by making use of the adapter module (106) to obtain the user's user credentials for the application from the identity provider.