Function authorization_sso_url 

fn authorization_sso_url(
    issuer: &str,
    idp_id: &str,
    req_id: &str,
) -> Result<Url>

Build the upstream SSO redirect URL for a pending authorization request.

The provider hands the browser back to the completion route carrying the request id, where the authorization code is minted. A trailing slash on the issuer is ignored.