use the existing SHA265 hash function

auth/oauth.go

 package oauth
 
 import (
-	"crypto/hmac"
-	"crypto/sha256"
-	"encoding/base64"
 	"github.com/aws/aws-sdk-go/aws"
+	"gitlab.bob.co.za/bob-public-utils/bobgroup-go-utils/encryption"
 	"math/rand"
 	"net/url"
 	"strconv"
@@ -55,7 +53,7 @@ func (auth Oauth1) GenerateAuthorizationHeader(method, requestUrl string) (Autho
 	// Build the signature
 	signatureBase := strings.ToUpper(method) + "&" + url.QueryEscape(strings.Split(requestUrl, "?")[0]) + "&" + url.QueryEscape(parameterString)
 	signingKey := url.QueryEscape(auth.ConsumerSecret) + "&" + url.QueryEscape(auth.AccessSecret)
-	signature := calculateSignature(signatureBase, signingKey)
+	signature := encryption.Hash(signatureBase, signingKey)
 
 	// Populate all the authorisation parameters
 	authParams := map[string]string{
@@ -77,13 +75,6 @@ func (auth Oauth1) GenerateAuthorizationHeader(method, requestUrl string) (Autho
 	return aws.String("OAuth " + strings.TrimSuffix(AuthorizationString, ",")), nil
 }
 
-func calculateSignature(base, key string) string {
-	hash := hmac.New(sha256.New, []byte(key))
-	hash.Write([]byte(base))
-	signature := hash.Sum(nil)
-	return base64.StdEncoding.EncodeToString(signature)
-}
-
 func generateNonce() string {
 	const allowed = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
 	b := make([]byte, 48)