Abstract: A method is provided for use in interworking a single sign-on authentication architecture and a further authentication architecture in a split terminal scenario. The split terminal scenario is one in which authentication under the single sign-on authentication architecture is required of a browsing agent (8) being used to access a relying party and in response, due to the interworking in the split terminal scenario, an associated authentication under the further authentication architecture is performed in relation to a separate authentication agent (7). A controlling agent (4) sends (C3) a token to the authentication agent (7). The controlling agent (4) sends (C4) a request to the browsing agent (8) to return a token for comparing with the token sent to the authentication agent (7).