Apply standard format, add dummy server

pkg/handler/metrics/metrics.go

@@ -0,0 +1,58 @@
+package metrics
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/rs/zerolog/log"
+)
+
+var (
+	// ErrInvalidToken is returned when the request token is invalid.
+	ErrInvalidToken = `Invalid or missing token`
+)
+
+// metrics gets initialized by New and provides the handler.
+type metrics struct {
+	token string
+}
+
+// ServeHTTP just implements the http.Handler interface.
+func (m metrics) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if m.token == "" {
+		promhttp.Handler().ServeHTTP(w, r)
+		return
+	}
+
+	header := r.Header.Get("Authorization")
+
+	if header == "" {
+		log.Debug().
+			Msg("Missing auth header")
+
+		http.Error(w, ErrInvalidToken, http.StatusUnauthorized)
+		return
+	}
+
+	if header != fmt.Sprintf("Bearer %s", m.token) {
+		log.Debug().
+			Msg("Invalid token provided")
+
+		http.Error(w, ErrInvalidToken, http.StatusUnauthorized)
+		return
+	}
+
+	promhttp.Handler().ServeHTTP(w, r)
+}
+
+// Handler returns the handler for metrics endpoint.
+func Handler(opts ...Option) http.Handler {
+	m := new(metrics)
+
+	for _, opt := range opts {
+		opt(m)
+	}
+
+	return m
+}

pkg/handler/metrics/option.go

@@ -0,0 +1,11 @@
+package metrics
+
+// Option configures an assets option.
+type Option func(*metrics)
+
+// WithToken returns an option to set a token.
+func WithToken(val string) Option {
+	return func(m *metrics) {
+		m.token = val
+	}
+}