add auth middleware

backend/middleware.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"net/http"
+	"os"
+)
+
+func authMiddleware(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+
+		expectedKey := os.Getenv("FRONTEND_API_KEY")
+		if expectedKey == "" {
+			http.Error(w, "server misconfigured", 500)
+			return
+		}
+
+		authHeader := r.Header.Get("Authorization")
+
+		expectedHeader := "Bearer " + expectedKey
+
+		if authHeader != expectedHeader {
+			http.Error(w, "unauthorized", http.StatusUnauthorized)
+			return
+		}
+
+		next.ServeHTTP(w, r)
+	})
+}