This tool can be used to build IdP-initiated single sign-on URLs compatible with Shibboleth Identity Provider.

While in most SSO cases, the process will be "kicked off" by the service sending a request to the IdP, the original SAML 1.0 and SAML 1.1 standards lacked the requisite specification for this flow, and as such support for initiation of the single sign on process was carried forward into the SAML 2.0 specification as "IDP-initiated", i.e. starting the SAML flow without an AuthnRequest.

This is also a useful tool for testing SAML integrations without requiring the Service Provider (SP) to have configured an integration on their end, as you can an create sample assertions for the SP integrators to see by kicking off an IdP-initiated SAML workflow, and capturing the SAMLResponse with a browser extension like SAML-Tracer for Firefox or SAML DevTools for Chrome.

For more details on IdP-initiated SSO with Shibboleth, see the Shib Wiki entry on the Unsolicited endpoint.