initial commit: Artifacto v0.1

Self-hosted HTML artifact publisher. Single Go binary, SQLite metadata,
HTML on disk. Features: password-protected artifacts, per-artifact expiration,
admin dashboard with view metrics (privacy-preserving daily-salt visitor hash,
sparklines, 30-day SVG chart, top referrers), rate-limited unlock endpoint.

Packaged as a Docker image (two-stage, CGO_ENABLED=0, pure-Go SQLite).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/auth/artifact.go

@@ -0,0 +1,80 @@
+package auth
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"net/http"
+	"strconv"
+	"strings"
+	"time"
+
+	"golang.org/x/crypto/bcrypt"
+)
+
+const unlockLifetime = 24 * time.Hour
+
+type Artifact struct {
+	secret []byte
+	secure bool
+}
+
+func NewArtifact(secretHex string, secure bool) *Artifact {
+	return &Artifact{secret: []byte(secretHex), secure: secure}
+}
+
+func HashPassword(p string) (string, error) {
+	b, err := bcrypt.GenerateFromPassword([]byte(p), bcrypt.DefaultCost)
+	return string(b), err
+}
+
+func VerifyPassword(hash, p string) bool {
+	return bcrypt.CompareHashAndPassword([]byte(hash), []byte(p)) == nil
+}
+
+func unlockCookieName(slug string) string {
+	return "artifacto_unlock_" + slug
+}
+
+func (a *Artifact) Issue(slug string) string {
+	issued := strconv.FormatInt(time.Now().Unix(), 10)
+	return issued + "." + a.sign(slug+"|"+issued)
+}
+
+func (a *Artifact) SetCookie(w http.ResponseWriter, slug string) {
+	http.SetCookie(w, &http.Cookie{
+		Name:     unlockCookieName(slug),
+		Value:    a.Issue(slug),
+		Path:     "/p/" + slug,
+		HttpOnly: true,
+		Secure:   a.secure,
+		SameSite: http.SameSiteLaxMode,
+		Expires:  time.Now().Add(unlockLifetime),
+	})
+}
+
+func (a *Artifact) Verify(r *http.Request, slug string) bool {
+	c, err := r.Cookie(unlockCookieName(slug))
+	if err != nil {
+		return false
+	}
+	parts := strings.SplitN(c.Value, ".", 2)
+	if len(parts) != 2 {
+		return false
+	}
+	issued, err := strconv.ParseInt(parts[0], 10, 64)
+	if err != nil {
+		return false
+	}
+	if time.Since(time.Unix(issued, 0)) > unlockLifetime {
+		return false
+	}
+	expected := a.sign(slug + "|" + parts[0])
+	return hmac.Equal([]byte(expected), []byte(parts[1]))
+}
+
+func (a *Artifact) sign(s string) string {
+	m := hmac.New(sha256.New, a.secret)
+	m.Write([]byte(s))
+	return base64.RawURLEncoding.EncodeToString(m.Sum(nil))
+}