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The SAML V2.0 Metadata Extensions for Registration and Publication Information is a specification for a set of extension elements to SAML metadata. These elements are particularly important for the purposes of interfederation. For exampleIn particular, every entity descriptor exported to eduGAIN must include the globally unique identifier of the registrar that registered that entity descriptor.
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According to the MD-RPI specification, the above extension element (and therefore the registrar's ID) may be inserted either at the aggregate level or the entity level. To accommodate per-entity metadata, the <mdrpi:RegistrationInfo> element has been is inserted at the entity level.
By definition, the <mdrpi:RegistrationInfo> element has an an optional <mdrpi:RegistrationPolicy> child element but the latter is not included in metadata registered by InCommon.
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As suggested earlier, the registrar ID in entity metadata may be used to formulate an IdP’s attribute release policy. Since software support for the <mdrpi:RegistrationInfo> element is spotty at best, the Registered By InCommon Category was created.
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