Add support for extended SANs on certificate requests

This commit adds supports for adding extended SANs like the permanent
identifier used in device attestation flows with CSRs. It was already
supported on certificates but not on certificate requests.

With this it will be possible to run:
  step certificate create --csr --template att.tpl \
  --kms "yubikey:?pin-value=123456" --key "yubikey:slot-id=82" \
  123456789 att.csr

Where att.tpl can be something like:
  {
    "subject": {{ toJson .Subject }},
    "sans": [{
      "type": "permanentIdentifier",
      "value": {{ toJson .Subject.CommonName }}
    }]
  }

x509util/certificate.go

@@ -71,7 +71,7 @@ func NewCertificate(cr *x509.CertificateRequest, opts ...Option) (*Certificate,
 	// Generate the subjectAltName extension if the certificate contains SANs
 	// that are not supported in the Go standard library.
 	if cert.hasExtendedSANs() && !cert.hasExtension(oidExtensionSubjectAltName) {
-		ext, err := createSubjectAltNameExtension(&cert, cert.Subject.IsEmpty())
+		ext, err := createCertificateSubjectAltNameExtension(cert, cert.Subject.IsEmpty())
 		if err != nil {
 			return nil, err
 		}

x509util/certificate_request.go

@@ -57,6 +57,19 @@ func NewCertificateRequest(signer crypto.Signer, opts ...Option) (*CertificateRe
 	}
 	cr.PublicKey = pub
 	cr.Signer = signer
+
+	// Generate the subjectAltName extension if the certificate contains SANs
+	// that are not supported in the Go standard library.
+	if cr.hasExtendedSANs() && !cr.hasExtension(oidExtensionSubjectAltName) {
+		ext, err := createCertificateRequestSubjectAltNameExtension(cr, cr.Subject.IsEmpty())
+		if err != nil {
+			return nil, err
+		}
+		// Prepend extension to achieve a certificate as similar as possible to
+		// the one generated by the Go standard library.
+		cr.Extensions = append([]Extension{ext}, cr.Extensions...)
+	}
+
 	return &cr, nil
 }
 
@@ -149,6 +162,30 @@ func (c *CertificateRequest) GetLeafCertificate() *Certificate {
 	return cert
 }
 
+// hasExtendedSANs returns true if the certificate contains any SAN types that
+// are not supported by the golang x509 library (i.e. RegisteredID, OtherName,
+// DirectoryName, X400Address, or EDIPartyName)
+//
+// See also https://datatracker.ietf.org/doc/html/rfc5280.html#section-4.2.1.6
+func (c *CertificateRequest) hasExtendedSANs() bool {
+	for _, san := range c.SANs {
+		if !(san.Type == DNSType || san.Type == EmailType || san.Type == IPType || san.Type == URIType || san.Type == AutoType || san.Type == "") {
+			return true
+		}
+	}
+	return false
+}
+
+// hasExtension returns true if the given extension oid is in the certificate.
+func (c *CertificateRequest) hasExtension(oid ObjectIdentifier) bool {
+	for _, e := range c.Extensions {
+		if e.ID.Equal(oid) {
+			return true
+		}
+	}
+	return false
+}
+
 // CreateCertificateRequest creates a simple X.509 certificate request with the
 // given common name and sans.
 func CreateCertificateRequest(commonName string, sans []string, signer crypto.Signer) (*x509.CertificateRequest, error) {

x509util/certificate_request_test.go

@@ -8,6 +8,8 @@ import (
 	"crypto/x509"
 	"crypto/x509/pkix"
 	"encoding/asn1"
+	"encoding/base64"
+	"fmt"
 	"net"
 	"net/url"
 	"reflect"
@@ -20,6 +22,49 @@ func TestNewCertificateRequest(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// ok extended sans
+	sans := []SubjectAlternativeName{
+		{Type: DNSType, Value: "foo.com"},
+		{Type: EmailType, Value: "root@foo.com"},
+		{Type: IPType, Value: "3.14.15.92"},
+		{Type: URIType, Value: "mailto:root@foo.com"},
+		{Type: PermanentIdentifierType, Value: "123456789"},
+	}
+	extendedSANs := CreateTemplateData("123456789", nil)
+	extendedSANs.SetSubjectAlternativeNames(sans...)
+	extendedSANsExtension, err := createSubjectAltNameExtension(nil, nil, nil, nil, sans, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// ok extended sans and extension
+	extendedSANsAndExtensionsTemplate := fmt.Sprintf(`{
+		"subject": {{ toJson .Subject }},
+		"sans": {{ toJson .SANs }},
+		"extensions": [
+			{"id":"2.5.29.17", "value":"%s"}
+		]
+	}`, base64.StdEncoding.EncodeToString(extendedSANsExtension.Value))
+
+	// ok permanent identifier template
+	permanentIdentifierTemplate := `{ 
+		"subject": {{ toJson .Subject }},
+		"sans": [{
+			"type": "permanentIdentifier", 
+			"value": {{ toJson .Subject.CommonName }}
+		}]
+	}`
+	permanentIdentifierTemplateExtension, err := createSubjectAltNameExtension(nil, nil, nil, nil, []SubjectAlternativeName{
+		{Type: PermanentIdentifierType, Value: "123456789"},
+	}, false)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// fail extended sans
+	failExtendedSANs := CreateTemplateData("123456789", nil)
+	failExtendedSANs.SetSubjectAlternativeNames(SubjectAlternativeName{Type: "badType", Value: "foo.com"})
+
 	type args struct {
 		signer crypto.Signer
 		opts   []Option
@@ -47,8 +92,50 @@ func TestNewCertificateRequest(t *testing.T) {
 			PublicKey: signer.Public(),
 			Signer:    signer,
 		}, false},
+		{"ok extended sans", args{signer, []Option{
+			WithTemplate(DefaultCertificateRequestTemplate, extendedSANs),
+		}}, &CertificateRequest{
+			Subject: Subject{CommonName: "123456789"},
+			SANs: []SubjectAlternativeName{
+				{Type: "dns", Value: "foo.com"},
+				{Type: "email", Value: "root@foo.com"},
+				{Type: "ip", Value: "3.14.15.92"},
+				{Type: "uri", Value: "mailto:root@foo.com"},
+				{Type: "permanentIdentifier", Value: "123456789"},
+			},
+			Extensions: []Extension{extendedSANsExtension},
+			PublicKey:  signer.Public(),
+			Signer:     signer,
+		}, false},
+		{"ok extended sans and extension", args{signer, []Option{
+			WithTemplate(extendedSANsAndExtensionsTemplate, extendedSANs),
+		}}, &CertificateRequest{
+			Subject: Subject{CommonName: "123456789"},
+			SANs: []SubjectAlternativeName{
+				{Type: "dns", Value: "foo.com"},
+				{Type: "email", Value: "root@foo.com"},
+				{Type: "ip", Value: "3.14.15.92"},
+				{Type: "uri", Value: "mailto:root@foo.com"},
+				{Type: "permanentIdentifier", Value: "123456789"},
+			},
+			Extensions: []Extension{extendedSANsExtension},
+			PublicKey:  signer.Public(),
+			Signer:     signer,
+		}, false},
+		{"ok permanent identifier template", args{signer, []Option{
+			WithTemplate(permanentIdentifierTemplate, CreateTemplateData("123456789", []string{})),
+		}}, &CertificateRequest{
+			Subject: Subject{CommonName: "123456789"},
+			SANs: []SubjectAlternativeName{
+				{Type: "permanentIdentifier", Value: "123456789"},
+			},
+			Extensions: []Extension{permanentIdentifierTemplateExtension},
+			PublicKey:  signer.Public(),
+			Signer:     signer,
+		}, false},
 		{"fail apply", args{signer, []Option{WithTemplateFile("testdata/missing.tpl", NewTemplateData())}}, nil, true},
 		{"fail unmarshal", args{signer, []Option{WithTemplate("{badjson", NewTemplateData())}}, nil, true},
+		{"fail extended sans", args{signer, []Option{WithTemplate(DefaultCertificateRequestTemplate, failExtendedSANs)}}, nil, true},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -58,7 +145,7 @@ func TestNewCertificateRequest(t *testing.T) {
 				return
 			}
 			if !reflect.DeepEqual(got, tt.want) {
-				t.Errorf("NewCertificateRequest() = %v, want %v", got, tt.want)
+				t.Errorf("NewCertificateRequest() = %+v, want %v", got, tt.want)
 			}
 		})
 	}

x509util/extensions.go

@@ -922,6 +922,14 @@ func (s *SerialNumber) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
+func createCertificateSubjectAltNameExtension(c Certificate, subjectIsEmpty bool) (Extension, error) {
+	return createSubjectAltNameExtension(c.DNSNames, c.EmailAddresses, c.IPAddresses, c.URIs, c.SANs, subjectIsEmpty)
+}
+
+func createCertificateRequestSubjectAltNameExtension(c CertificateRequest, subjectIsEmpty bool) (Extension, error) {
+	return createSubjectAltNameExtension(c.DNSNames, c.EmailAddresses, c.IPAddresses, c.URIs, c.SANs, subjectIsEmpty)
+}
+
 // createSubjectAltNameExtension will construct an Extension containing all
 // SubjectAlternativeNames held in a Certificate. It implements more types than
 // the golang x509 library, so it is used whenever OtherName or RegisteredID
@@ -931,11 +939,11 @@ func (s *SerialNumber) UnmarshalJSON(data []byte) error {
 //
 // TODO(mariano,unreality): X400Address, DirectoryName, and EDIPartyName types
 // are defined in RFC5280 but are currently unimplemented
-func createSubjectAltNameExtension(c *Certificate, subjectIsEmpty bool) (Extension, error) {
+func createSubjectAltNameExtension(dnsNames, emailAddresses MultiString, ipAddresses MultiIP, uris MultiURL, sans []SubjectAlternativeName, subjectIsEmpty bool) (Extension, error) {
 	var zero Extension
 
 	var rawValues []asn1.RawValue
-	for _, dnsName := range c.DNSNames {
+	for _, dnsName := range dnsNames {
 		rawValue, err := SubjectAlternativeName{
 			Type: DNSType, Value: dnsName,
 		}.RawValue()
@@ -946,7 +954,7 @@ func createSubjectAltNameExtension(c *Certificate, subjectIsEmpty bool) (Extensi
 		rawValues = append(rawValues, rawValue)
 	}
 
-	for _, emailAddress := range c.EmailAddresses {
+	for _, emailAddress := range emailAddresses {
 		rawValue, err := SubjectAlternativeName{
 			Type: EmailType, Value: emailAddress,
 		}.RawValue()
@@ -957,9 +965,9 @@ func createSubjectAltNameExtension(c *Certificate, subjectIsEmpty bool) (Extensi
 		rawValues = append(rawValues, rawValue)
 	}
 
-	for _, uri := range c.URIs {
+	for _, ip := range ipAddresses {
 		rawValue, err := SubjectAlternativeName{
-			Type: URIType, Value: uri.String(),
+			Type: IPType, Value: ip.String(),
 		}.RawValue()
 		if err != nil {
 			return zero, err
@@ -968,9 +976,9 @@ func createSubjectAltNameExtension(c *Certificate, subjectIsEmpty bool) (Extensi
 		rawValues = append(rawValues, rawValue)
 	}
 
-	for _, ip := range c.IPAddresses {
+	for _, uri := range uris {
 		rawValue, err := SubjectAlternativeName{
-			Type: IPType, Value: ip.String(),
+			Type: URIType, Value: uri.String(),
 		}.RawValue()
 		if err != nil {
 			return zero, err
@@ -979,7 +987,7 @@ func createSubjectAltNameExtension(c *Certificate, subjectIsEmpty bool) (Extensi
 		rawValues = append(rawValues, rawValue)
 	}
 
-	for _, san := range c.SANs {
+	for _, san := range sans {
 		rawValue, err := san.RawValue()
 		if err != nil {
 			return zero, err