Create file sp-metadata.xml in the below path:

/var/www/html/sp-metadata.xml

The entityId attribute specifies who we are:

  <md:EntityDescriptor xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata" xmlns:ds="http://www.w3.org/2000/09/xmldsig#" entityID="https://your hostname">
    <md:SPSSODescriptor AuthnRequestsSigned="true" WantAssertionsSigned="true" protocolSupportEnumeration="urn:oasis:names:tc:SAML:2.0:protocol">

The <ds:X509Certificate> element contains the public key that was generated earlier:

      <md:KeyDescriptor>
        <ds:KeyInfo>
          <ds:X509Data>
            <ds:X509Certificate>ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopqrstuvwyz01234567890+/A
              ABCDEFGHIJKLMNOPQRSTUVWYZabcdefghijklmnopq==
            </ds:X509Certificate>
          </ds:X509Data>
        </ds:KeyInfo>
      </md:KeyDescriptor>

the "Location" xml attribute specifies the URL at which the IdP will post the user info after a successful login:   

 <md:AssertionConsumerService Binding="urn:oasis:names:tc:SAML:2.0:bindings:HTTP-POST" Location="https://[your hostname]/Shibboleth.sso/SAML2/POST" index="1"/>
  </md:SPSSODescriptor>
</md:EntityDescriptor>

Next Step:

SHRINE 4.0.0 Appendix A.7 - More Details: Shrine Configuration for SSO