telemetry: add tracing

- telemetry/tace: add traces throughout code
- telemetry/metrics: nest metrics and trace under telemetry
- telemetry/tace: add service name span to HTTPMetricsHandler.
- telemetry/metrics: removed chain dependency middleware_tests.
- telemetry/metrics: wrap and encapsulate variatic view registration.
- telemetry/tace: add jaeger support for tracing.
- cmd/pomerium: move `parseOptions` to internal/config.
- cmd/pomerium: offload server handling to httputil and sub pkgs.
- httputil: standardize creation/shutdown of http listeners.
- httputil: prefer curve X25519 to P256 when negotiating TLS.
- fileutil: use standardized Getw

Signed-off-by: Bobby DeSimone <bobbydesimone@gmail.com>

internal/telemetry/metrics/providers.go

@@ -0,0 +1,39 @@
+package metrics // import "github.com/pomerium/pomerium/internal/telemetry/metrics"
+
+import (
+	"fmt"
+	"net/http"
+
+	ocprom "contrib.go.opencensus.io/exporter/prometheus"
+	prom "github.com/prometheus/client_golang/prometheus"
+	"go.opencensus.io/stats/view"
+)
+
+// PrometheusHandler creates an exporter that exports stats to Prometheus
+// and returns a handler suitable for exporting metrics.
+func PrometheusHandler() (http.Handler, error) {
+	if err := registerDefaultViews(); err != nil {
+		return nil, fmt.Errorf("internal/telemetry: failed registering views")
+	}
+	reg := prom.DefaultRegisterer.(*prom.Registry)
+	exporter, err := ocprom.NewExporter(
+		ocprom.Options{
+			Namespace: "pomerium",
+			Registry:  reg,
+		})
+	if err != nil {
+		return nil, fmt.Errorf("internal/telemetry: prometheus exporter: %v", err)
+	}
+	view.RegisterExporter(exporter)
+	mux := http.NewServeMux()
+	mux.Handle("/metrics", exporter)
+	return mux, nil
+}
+
+func registerDefaultViews() error {
+	var views []*view.View
+	for _, v := range DefaultViews {
+		views = append(views, v...)
+	}
+	return view.Register(views...)
+}