feat: add backend jwt middleware

backend/internal/auth/middleware.go

@@ -0,0 +1,49 @@
+package auth
+
+import (
+	"encoding/json"
+	"net/http"
+	"strings"
+)
+
+type Middleware struct {
+	validator *Validator
+}
+
+func NewMiddleware(validator *Validator) Middleware {
+	return Middleware{validator: validator}
+}
+
+func (m Middleware) RequireAuth(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		token, ok := bearerToken(r.Header.Get("Authorization"))
+		if !ok {
+			writeUnauthorized(w)
+			return
+		}
+
+		principal, err := m.validator.Validate(r.Context(), token)
+		if err != nil {
+			writeUnauthorized(w)
+			return
+		}
+
+		next.ServeHTTP(w, r.WithContext(withPrincipal(r.Context(), principal)))
+	})
+}
+
+func bearerToken(header string) (string, bool) {
+	const prefix = "Bearer "
+	if !strings.HasPrefix(header, prefix) {
+		return "", false
+	}
+
+	token := strings.TrimSpace(strings.TrimPrefix(header, prefix))
+	return token, token != ""
+}
+
+func writeUnauthorized(w http.ResponseWriter) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(http.StatusUnauthorized)
+	_ = json.NewEncoder(w).Encode(map[string]string{"error": "unauthorized"})
+}