Abstract: An authentication system is disclosed for use in authenticating an entity to a relying party, to enable the entity to access a protected resource provided by the relying party via a web page, comprising an authentication component installable in a web browser used by the entity to access the web page, the authentication component comprising (a) a page scanner component which is operable when the entity accesses the web page to scan the web page (and/or to ask the entity) to identify a plurality of authentication systems supported by the web page; and (b) an activator component which is operable when the entity accesses the web page to install an identity system selector component in the web page which is operable to interact with the entity to enable the entity to select which of the plurality of authentication systems to use.