Integrate email notifications into signup and login (#38)

backend/product/auth/http/public/metrics.go

@@ -0,0 +1,35 @@
+package public
+
+import (
+	"net/http"
+	"time"
+
+	sresponse "git.sendico.io/tech/sxchnge/product/auth/response"
+	"github.com/go-chi/chi/v5/middleware"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var flowRequests = promauto.NewCounterVec(prometheus.CounterOpts{Name: "sxchnge_auth_flow_requests_total", Help: "Authentication flow outcomes; success means this HTTP step completed, not email delivery."}, []string{"operation", "outcome"})
+var flowDuration = promauto.NewHistogramVec(prometheus.HistogramOpts{Name: "sxchnge_auth_flow_duration_seconds", Help: "Authentication HTTP step latency."}, []string{"operation"})
+
+func measured(operation string, handler sresponse.HandlerFunc) sresponse.HandlerFunc {
+	return func(r *http.Request) http.HandlerFunc {
+		start := time.Now()
+		response := handler(r)
+		return func(w http.ResponseWriter, r *http.Request) {
+			wrapped := middleware.NewWrapResponseWriter(w, r.ProtoMajor)
+			response(wrapped, r)
+			outcome := "accepted"
+			if wrapped.Status() >= 500 {
+				outcome = "unavailable"
+			} else if wrapped.Status() == 429 {
+				outcome = "limited"
+			} else if wrapped.Status() >= 400 {
+				outcome = "rejected"
+			}
+			flowRequests.WithLabelValues(operation, outcome).Inc()
+			flowDuration.WithLabelValues(operation).Observe(time.Since(start).Seconds())
+		}
+	}
+}