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This simple example already highlights some differences between a SAML-based solution and an UMA-based solution. Note that functions performed by the WP App in the SAML model are carried out by more than one component in the UMA model. This helps explain the need for a protocol for cooperatively provided services in the UMA model–The Resource Server and Authorization Server need to collaborate to accomplish the usage scenario. Conversely the comparison highlights that some elements of the usage scenario are "out of band" with respect to the SAML model. A full solution would have to be "SAML plus".
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