use email from SAN (sigstore#288)

Signed-off-by: Asra Ali <asraa@google.com>

Author: asraa

pkg/pki/x509/x509.go

@@ -30,6 +30,8 @@ import (
 	"io"
 	"io/ioutil"
 	"strings"
+
+	"github.com/go-playground/validator"
 )
 
 // EmailAddressOID defined by https://oidref.com/1.2.840.113549.1.9.1
@@ -176,9 +178,11 @@ func (k PublicKey) CanonicalValue() ([]byte, error) {
 func (k PublicKey) EmailAddresses() []string {
 	var names []string
 	if k.cert != nil {
-		for _, name := range k.cert.c.Subject.Names {
-			if name.Type.Equal(EmailAddressOID) {
-				names = append(names, strings.ToLower(name.Value.(string)))
+		for _, name := range k.cert.c.EmailAddresses {
+			validate := validator.New()
+			errs := validate.Var(name, "required,email")
+			if errs == nil {
+				names = append(names, strings.ToLower(name))
 			}
 		}
 	}

tests/x509.go

@@ -47,21 +47,24 @@ baT2ax2dXBcpInWaFESqGF35KISflP1EmMvEnfG+AzHecQ0WQp5QzNId+w==
 // Generated with:
 // openssl req -newkey rsa:2048 -nodes -keyout test.key -x509 -out test.crt
 const rsaCert = `-----BEGIN CERTIFICATE-----
-MIICujCCAaICCQDV0chJ/QVmCTANBgkqhkiG9w0BAQsFADAfMR0wGwYJKoZIhvcN
-AQkBFg50ZXN0QHJla29yLmRldjAeFw0yMTAyMjAxOTUyMTZaFw0yMTAzMjIxOTUy
-MTZaMB8xHTAbBgkqhkiG9w0BCQEWDnRlc3RAcmVrb3IuZGV2MIIBIjANBgkqhkiG
-9w0BAQEFAAOCAQ8AMIIBCgKCAQEA3wqI/TysUiKTgY1bz+wdJfEOil4MEsRASKGz
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+BmU8k2FeTuqV15piPCE=
 -----END CERTIFICATE-----`
 
 const rsaKey = `-----BEGIN PRIVATE KEY-----