From 3776c26a72aa8ab61b77f53528dc807990ff54bf Mon Sep 17 00:00:00 2001
From: Stanislav Paskalev <kshorg@gmail.com>
Date: Sat, 16 Sep 2017 17:47:46 +0300
Subject: [PATCH] Initial support for SHa-256 and SHA-512/256

---
 digest.go    | 17 ++++++++++++-----
 misc.go      | 28 ++++++++++++++++++++++++++--
 misc_test.go |  4 ++--
 3 files changed, 40 insertions(+), 9 deletions(-)

diff --git a/digest.go b/digest.go
index 21b0933..e7c8467 100644
--- a/digest.go
+++ b/digest.go
@@ -20,6 +20,7 @@ type digest_client struct {
 }
 
 type DigestAuth struct {
+	Algorithm        string
 	Realm            string
 	Opaque           string
 	Secrets          SecretProvider
@@ -91,8 +92,8 @@ func (a *DigestAuth) RequireAuth(w http.ResponseWriter, r *http.Request) {
 	a.clients[nonce] = &digest_client{nc: 0, last_seen: time.Now().UnixNano()}
 	w.Header().Set(contentType, a.Headers.V().UnauthContentType)
 	w.Header().Set(a.Headers.V().Authenticate,
-		fmt.Sprintf(`Digest realm="%s", nonce="%s", opaque="%s", algorithm="MD5", qop="auth"`,
-			a.Realm, nonce, a.Opaque))
+		fmt.Sprintf(`Digest realm="%s", nonce="%s", opaque="%s", algorithm="%s", qop="auth"`,
+			a.Realm, nonce, a.Opaque, a.Algorithm))
 	w.WriteHeader(a.Headers.V().UnauthCode)
 	w.Write([]byte(a.Headers.V().UnauthResponse))
 }
@@ -138,7 +139,12 @@ func (da *DigestAuth) CheckAuth(r *http.Request) (username string, authinfo *str
 	if _, ok := auth["algorithm"]; !ok {
 		auth["algorithm"] = "MD5"
 	}
-	if da.Opaque != auth["opaque"] || auth["algorithm"] != "MD5" || auth["qop"] != "auth" {
+	if da.Opaque != auth["opaque"] || auth["qop"] != "auth" {
+		return "", nil
+	}
+
+	H, ok := algorithms[strings.ToUpper(auth["algorithm"])]
+	if !ok {
 		return "", nil
 	}
 
@@ -255,14 +261,15 @@ func (a *DigestAuth) NewContext(ctx context.Context, r *http.Request) context.Co
 		nonce := RandomKey()
 		a.clients[nonce] = &digest_client{nc: 0, last_seen: time.Now().UnixNano()}
 		info.ResponseHeaders.Set(a.Headers.V().Authenticate,
-			fmt.Sprintf(`Digest realm="%s", nonce="%s", opaque="%s", algorithm="MD5", qop="auth"`,
-				a.Realm, nonce, a.Opaque))
+			fmt.Sprintf(`Digest realm="%s", nonce="%s", opaque="%s", algorithm="%s", qop="auth"`,
+				a.Realm, nonce, a.Opaque, a.Algorithm))
 	}
 	return context.WithValue(ctx, infoKey, info)
 }
 
 func NewDigestAuthenticator(realm string, secrets SecretProvider) *DigestAuth {
 	da := &DigestAuth{
+		Algorithm:            "MD5", // NOT RECOMMENDED according to RFC 7616
 		Opaque:               RandomKey(),
 		Realm:                realm,
 		Secrets:              secrets,
diff --git a/misc.go b/misc.go
index 4536ce6..179adfb 100644
--- a/misc.go
+++ b/misc.go
@@ -4,12 +4,22 @@ import (
 	"bytes"
 	"crypto/md5"
 	"crypto/rand"
+	"crypto/sha256"
+	"crypto/sha512"
 	"encoding/base64"
 	"fmt"
 	"net/http"
 	"strings"
 )
 
+var (
+	algorithms = map[string]func(string) string{
+		"MD5":         MD5,
+		"SHA-256":     SHA_256,
+		"SHA-512/256": SHA_512_256,
+	}
+)
+
 // RandomKey returns a random 16-byte base64 alphabet string
 func RandomKey() string {
 	k := make([]byte, 12)
@@ -23,13 +33,27 @@ func RandomKey() string {
 	return base64.StdEncoding.EncodeToString(k)
 }
 
-// H function for MD5 algorithm (returns a lower-case hex MD5 digest)
-func H(data string) string {
+// Hashes data using MD5 and returns a lower-case hex digest
+func MD5(data string) string {
 	digest := md5.New()
 	digest.Write([]byte(data))
 	return fmt.Sprintf("%x", digest.Sum(nil))
 }
 
+// Hashes data using SHA-256 and returns a lower-case hex digest
+func SHA_256(data string) string {
+	digest := sha256.New()
+	digest.Write([]byte(data))
+	return fmt.Sprintf("%x", digest.Sum(nil))
+}
+
+// Hashes data using SHA-512/256 and returns a lower-case hex digest
+func SHA_512_256(data string) string {
+	digest := sha512.New512_256()
+	digest.Write([]byte(data))
+	return fmt.Sprintf("%x", digest.Sum(nil))
+}
+
 // ParseList parses a comma-separated list of values as described by
 // RFC 2068 and returns list elements.
 //
diff --git a/misc_test.go b/misc_test.go
index 31a920f..c1b45a0 100644
--- a/misc_test.go
+++ b/misc_test.go
@@ -5,10 +5,10 @@ import (
 	"testing"
 )
 
-func TestH(t *testing.T) {
+func TestMD5(t *testing.T) {
 	const hello = "Hello, world!"
 	const hello_md5 = "6cd3556deb0da54bca060b4c39479839"
-	h := H(hello)
+	h := MD5(hello)
 	if h != hello_md5 {
 		t.Fatal("Incorrect digest for test string:", h, "instead of", hello_md5)
 	}