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For this very basic adoption using the DSX Discovery Service as central discovery service, everything an SP needs to know is the URL that the discovery service uses to serve SAML2 IdP discovery requests. Consult the documentation of the SAML SP product you are using on how to apply Discovery Service URL. If you are for example using the Shibboleth SP, consult the Shibboleth documentation ("discoveryURL") or in case of SimpleSAMLphp the SimpleSAMLphp documentation on this topic ("discoURL"). Generic information on the SAML2 IdP Discovery Service protocol are available in the Identity Provider Discovery Service Protocol and Profile.
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The disadvantage of using a central discovery service is that users are redirected to another host, which has a different look and feel . Also, some users might be confused that they were sent away from the service they intended to usefrom both the SP they intend to log in to as well as the IDP they intend to log in from.
Screencast to configure Discovery Service with Sibboleth SP
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