use email from SAN (#288)

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

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
-JddZ6x9hb+rn2UVoJmuxN62XI0TMoMn4mukgfCgY6jgTB58V+/LaeSA8Wz1p4gOx
-hk1mcgbF4HyxR+xlRgYfH4iSbXy+Ez/8ZjM2OO68fKr4JZEA5LXZkhJr32JqH+Ui
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-SIb3DQEBCwUAA4IBAQCe/lpUhsJVRkwXfndUEqiGVoPApGpwFMg4l1UnlPcbDXGV
-+z564uZlS0LyjsJjaalP/CJ9R+DO5dpRcKmBzBbMHjGSqoFW/ZIUm8Yybnd2eC7b
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-l7ArJO7hmz6eJON+xDbhcYtAOavUqbT+fVcgi2qm
+MIIDOjCCAiKgAwIBAgIUEP925shVBKERFCsymdSqESLZFyMwDQYJKoZIhvcNAQEL
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+BmU8k2FeTuqV15piPCE=
 -----END CERTIFICATE-----`
 
 const rsaKey = `-----BEGIN PRIVATE KEY-----