Add TLS support via the exporter toolkit

Metrics may contain sensitive information, so it should be possible to
scrape them over an encrypted connection. This requires TLS support.
For consistency with other Prometheus exporters, we use the exporter
toolkit to provide TLS support.

Fixes prometheus#413.

README.md

@@ -112,9 +112,9 @@ NOTE: Version 0.7.0 switched to the [kingpin](https://github.com/alecthomas/king
     Flags:
       -h, --help                    Show context-sensitive help (also try
                                     --help-long and --help-man).
-          --web.listen-address=":9102"
-                                    The address on which to expose the web interface
-                                    and generated Prometheus metrics.
+          --web.listen-address=:9102 ...  
+                                Addresses on which to expose metrics and web interface. Repeatable for multiple addresses.
+          --web.config.file=""      [EXPERIMENTAL] Path to configuration file that can enable TLS or authentication.
           --web.enable-lifecycle    Enable shutdown and reload via HTTP request.
           --web.telemetry-path="/metrics"
                                     Path under which to expose metrics.
@@ -171,6 +171,10 @@ NOTE: Version 0.7.0 switched to the [kingpin](https://github.com/alecthomas/king
           --version                 Show application version.
     ```
 
+## TLS support
+
+TLS support is provided via the [Prometheus Exporter Toolkit](https://github.com/prometheus/exporter-toolkit). Please see [its configuration documentation]9https://github.com/prometheus/exporter-toolkit/blob/master/docs/web-configuration.md) for how to configure TLS.
+
 ## Lifecycle API
 
 The `statsd_exporter` has an optional lifecycle API (disabled by default) that can be used to reload or quit the exporter 

go.mod

@@ -8,6 +8,7 @@ require (
 	github.com/prometheus/client_golang v1.13.0
 	github.com/prometheus/client_model v0.2.0
 	github.com/prometheus/common v0.37.0
+	github.com/prometheus/exporter-toolkit v0.8.1
 	github.com/stvp/go-udp-testing v0.0.0-20201019212854-469649b16807
 	gopkg.in/alecthomas/kingpin.v2 v2.2.6
 	gopkg.in/yaml.v2 v2.4.0
@@ -18,10 +19,20 @@ require (
 	github.com/alecthomas/units v0.0.0-20211218093645-b94a6e3cc137 // indirect
 	github.com/beorn7/perks v1.0.1 // indirect
 	github.com/cespare/xxhash/v2 v2.1.2 // indirect
+	github.com/coreos/go-systemd/v22 v22.4.0 // indirect
 	github.com/go-logfmt/logfmt v0.5.1 // indirect
 	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/jpillora/backoff v1.0.0 // indirect
 	github.com/matttproud/golang_protobuf_extensions v1.0.1 // indirect
+	github.com/mwitkow/go-conntrack v0.0.0-20190716064945-2f068394615f // indirect
 	github.com/prometheus/procfs v0.8.0 // indirect
-	golang.org/x/sys v0.0.0-20220708085239-5a0f0661e09d // indirect
+	golang.org/x/crypto v0.0.0-20221012134737-56aed061732a // indirect
+	golang.org/x/net v0.0.0-20220909164309-bea034e7d591 // indirect
+	golang.org/x/oauth2 v0.0.0-20220909003341-f21342109be1 // indirect
+	golang.org/x/sync v0.1.0 // indirect
+	golang.org/x/sys v0.0.0-20220728004956-3c1f35247d10 // indirect
+	golang.org/x/text v0.3.7 // indirect
+	google.golang.org/appengine v1.6.7 // indirect
 	google.golang.org/protobuf v1.28.1 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
 )