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As your IdP will need act as an SP, you'll need extra blocks in your entity's metadata. Update Create a new sp-metadata.xml or update your existing idp-metadata.xml file to include a <SPSSODescriptor> block. You'll need to copy the signing and encryption certificates from the IdP part of the metadata and replace the base URI (https://idp.example.ac.uk/idp) with the base of your IdP.
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