Implement digest header generation

Signed-off-by: Knut Ahlers <knut@ahlers.me>

http/digest.go

@@ -0,0 +1,55 @@
+package http
+
+import (
+	"crypto/md5"
+	"crypto/rand"
+	"encoding/hex"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+
+	"github.com/Luzifer/go_helpers/str"
+)
+
+func GetDigestAuth(resp *http.Response, method, requestPath, user, password string) string {
+	params := map[string]string{}
+	for _, part := range strings.Split(resp.Header.Get("Www-Authenticate"), " ") {
+		if !strings.Contains(part, `="`) {
+			continue
+		}
+		spl := strings.Split(strings.Trim(part, " ,"), "=")
+		if !str.StringInSlice(spl[0], []string{"nonce", "realm", "qop"}) {
+			continue
+		}
+		params[spl[0]] = strings.Trim(spl[1], `"`)
+	}
+
+	b := make([]byte, 8)
+	io.ReadFull(rand.Reader, b)
+
+	params["cnonce"] = fmt.Sprintf("%x", b)
+	params["nc"] = "1"
+	params["uri"] = requestPath
+	params["username"] = user
+	params["response"] = getMD5([]string{
+		getMD5([]string{params["username"], params["realm"], password}),
+		params["nonce"],
+		params["nc"],
+		params["cnonce"],
+		params["qop"],
+		getMD5([]string{method, requestPath}),
+	})
+
+	authParts := []string{}
+	for k, v := range params {
+		authParts = append(authParts, fmt.Sprintf("%s=%q", k, v))
+	}
+	return "Digest " + strings.Join(authParts, ", ")
+}
+
+func getMD5(in []string) string {
+	h := md5.New()
+	h.Write([]byte(strings.Join(in, ":")))
+	return hex.EncodeToString(h.Sum(nil))
+}