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Expanding on the latter pair of requirements: Assume at least 80% of the users that visit the SP are presented with a discovery interface that includes one of their preferred IdPs, and moreover, the IdP selected by the user meets the assurance and attribute requirements without further human interaction. Remember, this must result in a positive user experience at least 80% of the time!
Today of course we are far from meeting the needs of this use case. SPs either manually board IdPs one-by-one, leading to a relatively small group of trusted IdPs, or SPs present the user with a broad selection of IdPs, few of which meet the designated assurance and attribute requirements. In either case, the SP realizes roughly a 20% success rate (at best). Not good.
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