added hmac jsvm primitives and updated docs

tools/security/crypto.go

@@ -1,9 +1,11 @@
 package security
 
 import (
+	"crypto/hmac"
 	"crypto/md5"
 	"crypto/sha256"
 	"crypto/sha512"
+	"crypto/subtle"
 	"encoding/base64"
 	"fmt"
 	"strings"
@@ -39,3 +41,22 @@ func SHA512(text string) string {
 	h.Write([]byte(text))
 	return fmt.Sprintf("%x", h.Sum(nil))
 }
+
+// HS256 creates a HMAC hash with sha256 digest algorithm.
+func HS256(text string, secret string) string {
+	h := hmac.New(sha256.New, []byte(secret))
+	h.Write([]byte(text))
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+// HS512 creates a HMAC hash with sha512 digest algorithm.
+func HS512(text string, secret string) string {
+	h := hmac.New(sha512.New, []byte(secret))
+	h.Write([]byte(text))
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+// Equal compares two hash strings for equality without leaking timing information.
+func Equal(hash1 string, hash2 string) bool {
+	return subtle.ConstantTimeCompare([]byte(hash1), []byte(hash2)) == 1
+}