Replacing fastsha256 with crypto/sha256 package from golang standard package (#1584)

signature-v4-utils.go

@@ -18,13 +18,12 @@ package main
 
 import (
 	"crypto/hmac"
+	"crypto/sha256"
 	"encoding/hex"
 	"net/http"
 	"regexp"
 	"strings"
 	"unicode/utf8"
-
-	fastSha256 "github.com/minio/minio/pkg/crypto/sha256"
 )
 
 // isValidRegion - verify if incoming region value is valid with configured Region.
@@ -42,7 +41,7 @@ func isValidRegion(reqRegion string, confRegion string) bool {
 
 // sumHMAC calculate hmac between two input byte array.
 func sumHMAC(key []byte, data []byte) []byte {
-	hash := hmac.New(fastSha256.New, key)
+	hash := hmac.New(sha256.New, key)
 	hash.Write(data)
 	return hash.Sum(nil)
 }