The Writer Service URL is used by the identity provider. After successful authentication, the common domain cookie is appended with the query parameter _liberty_idp=entity-ID-of-identity-provider. This parameter is used to redirect the principal to the ID-FF Writer Service URL defined for the identity provider. The URL is configured as the value for the ID-FF Writer Service URL attribute when a circle of trust is created. Use the format http://idp-introduction-host:port/deployment-uri/idffwriter where idp-introduction-host:port refers to the machine on which the ID-FF Identity Provider Introduction service is installed and deployment-uri tells the web container where to look for information specific to the application (such as classes or JARs).