utility for extracting SSO data

go.mod

module keycloak-idp-phase2

go 1.21.5

keycloak-idp-phase2.go

package main

// keycloak-id-phase2 a small utility to extract useful info from the XML
// metadata returned by clinics when integrating SSO.
//
// git clone git@gist.github.com:34a7d19af71c254afb0b7dba9990f597.git keycloak-idp-phase2
//
//   $ ./keycloak-idp-phase2 < metadata.xml

import (
	"crypto/x509"
	"encoding/base64"
	"encoding/xml"
	"flag"
	"fmt"
	"log"
	"net/url"
	"os"
	"regexp"
	"strings"
)

var PostBindingRE = regexp.MustCompile(`bindings:HTTP-POST`)

type Metadata struct {
	SigningCert struct {
		Data string `xml:",innerxml"`
	} `xml:"IDPSSODescriptor>KeyDescriptor>KeyInfo>X509Data>X509Certificate"`
	SSOServices []struct {
		Binding  string `xml:",attr"`
		Location string `xml:",attr"`
	} `xml:"IDPSSODescriptor>SingleSignOnService"`
}

// parseCert makes sure that the certificate data is parseable.
func parseCert(cert string) (*x509.Certificate, error) {
	der, err := base64.StdEncoding.DecodeString(strings.TrimSpace(cert))
	if err != nil {
		return nil, fmt.Errorf("base64 decoding: %w", err)
	}

	parsed, err := x509.ParseCertificate(der)
	if err != nil {
		return nil, fmt.Errorf("parsing certificate data: %w", err)
	}

	return parsed, nil
}

// validateCertAndURL ensures that the signing certificate applies to the SSO
// Service URL.
func validateCertAndURL(cert *x509.Certificate, ssoServiceURL string) error {
	ssoURL, err := url.Parse(ssoServiceURL)
	if err != nil {
		return fmt.Errorf("SSO service location failed to parse: %s", err)
	} else {
		if err := cert.VerifyHostname(ssoURL.Host); err != nil {
			return fmt.Errorf("certificate isn't valid for SSO service location: %s", err)
		}
	}
	return nil
}

func main() {
	var xmlFilename string
	flag.StringVar(&xmlFilename, "xml-filename", "-", "the XML metadata from the SSO partner clinic")
	flag.Parse()

	var f *os.File = os.Stdin
	if xmlFilename != "-" {
		xmlFile, err := os.Open(xmlFilename)
		if err != nil {
			log.Fatalf("opening XML filename %q: %s", xmlFilename, err)
		}
		defer xmlFile.Close()
		f = xmlFile
	}

	metadata := &Metadata{}
	if err := xml.NewDecoder(f).Decode(&metadata); err != nil {
		log.Fatal("parsing XML: %s", err)
	}

	var ssoServiceLocation string
	for _, ssoService := range metadata.SSOServices {
		if PostBindingRE.MatchString(ssoService.Binding) {
			ssoServiceLocation = ssoService.Location
		}
	}
	if strings.TrimSpace(ssoServiceLocation) == "" {
		log.Fatal("no SSO service location found")
	}

	trimmedCert := strings.TrimSpace(metadata.SigningCert.Data)
	if trimmedCert == "" {
		log.Fatal("no X509 signing certificate found")
	}

	cert, err := parseCert(trimmedCert)
	if err != nil {
		log.Fatal("X509 signing certificate failed to parse: %s", err)
	}
	if cert == nil {
		log.Fatal("no X509 certificate (this shouldn't happen!)")
	}
	if err := validateCertAndURL(cert, ssoServiceLocation); err != nil {
		log.Fatal(err)
	}

	fmt.Printf("single_sign_on_service_url = \"%s\"\n", ssoServiceLocation)
	fmt.Printf("signing_certificate = \"%s\"\n", strings.TrimSpace(metadata.SigningCert.Data))
}