func DefaultOnError(w http.ResponseWriter, r *http.Request, err error) {
	if parseErr, ok := err.(*saml.InvalidResponseError); ok {
		log.Printf("WARNING: received invalid saml response: %s (now: %s) %s",
			parseErr.Response, parseErr.Now, parseErr.PrivateErr)
	} else {
		log.Printf("ERROR: %s", err)
	}
	http.Error(w, http.StatusText(http.StatusForbidden), http.StatusForbidden)
}
DefaultOnError is the default ErrorFunction implementation. It prints
an message via the standard log package and returns a simple text
"Forbidden" message to the user.
package samlsp
import (
	"log"
	"net/http"
	"github.com/crewjam/saml"
)
type ErrorFunction func(w http.ResponseWriter, r *http.Request, err error)