S7evinK: basicauth metrics (#961)

* Add setting to enable/disable metrics (#461)
Add basic auth to /metric handlers

Signed-off-by: Till Faelligen <tfaelligen@gmail.com>

* Add warning message if metrics are exposed without protection

* Remove redundant type conversion

Signed-off-by: Till Faelligen <tfaelligen@gmail.com>

* SetBasicAuth per test case

* Update warning message and change loglevel to warn

* Update common/config/config.go

* Update dendrite-config.yaml

Co-authored-by: Till Faelligen <tfaelligen@gmail.com>
Co-authored-by: Neil Alexander <neilalexander@users.noreply.github.com>

6 files changed, 155 insertions, 5 deletions

diff --git a/cmd/dendrite-monolith-server/main.go b/cmd/dendrite-monolith-server/main.go
index 9f6531ed..c71d956b 100644
--- a/cmd/dendrite-monolith-server/main.go
+++ b/cmd/dendrite-monolith-server/main.go
@@ -33,8 +33,8 @@ import (
 	"github.com/matrix-org/dendrite/publicroomsapi"
 	"github.com/matrix-org/dendrite/roomserver"
 	"github.com/matrix-org/dendrite/syncapi"
-
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+
 	"github.com/sirupsen/logrus"
 )
 
@@ -78,7 +78,9 @@ func main() {
 
 	// Set up the API endpoints we handle. /metrics is for prometheus, and is
 	// not wrapped by CORS, while everything else is
-	http.Handle("/metrics", promhttp.Handler())
+	if cfg.Metrics.Enabled {
+		http.Handle("/metrics", common.WrapHandlerInBasicAuth(promhttp.Handler(), cfg.Metrics.BasicAuth))
+	}
 	http.Handle("/", httpHandler)
 
 	// Expose the matrix APIs directly rather than putting them under a /api path.
diff --git a/common/basecomponent/base.go b/common/basecomponent/base.go
index 432819a2..dc27f540 100644
--- a/common/basecomponent/base.go
+++ b/common/basecomponent/base.go
@@ -208,7 +208,7 @@ func (b *BaseDendrite) SetupAndServeHTTP(bindaddr string, listenaddr string) {
 		addr = listenaddr
 	}
 
-	common.SetupHTTPAPI(http.DefaultServeMux, common.WrapHandlerInCORS(b.APIMux))
+	common.SetupHTTPAPI(http.DefaultServeMux, common.WrapHandlerInCORS(b.APIMux), b.Cfg)
 	logrus.Infof("Starting %s server on %s", b.componentName, addr)
 
 	err := http.ListenAndServe(addr, nil)
diff --git a/common/config/config.go b/common/config/config.go
index e2f5e663..a1a84425 100644
--- a/common/config/config.go
+++ b/common/config/config.go
@@ -119,6 +119,19 @@ type Dendrite struct {
 		ThumbnailSizes []ThumbnailSize `yaml:"thumbnail_sizes"`
 	} `yaml:"media"`
 
+	// The configuration to use for Prometheus metrics
+	Metrics struct {
+		// Whether or not the metrics are enabled
+		Enabled bool `yaml:"enabled"`
+		// Use BasicAuth for Authorization
+		BasicAuth struct {
+			// Authorization via Static Username & Password
+			// Hardcoded Username and Password
+			Username string `yaml:"username"`
+			Password string `yaml:"password"`
+		} `yaml:"basic_auth"`
+	} `yaml:"metrics"`
+
 	// The configuration for talking to kafka.
 	Kafka struct {
 		// A list of kafka addresses to connect to.
diff --git a/common/httpapi.go b/common/httpapi.go
index 22c77447..843336f5 100644
--- a/common/httpapi.go
+++ b/common/httpapi.go
@@ -6,6 +6,7 @@ import (
 
 	"github.com/matrix-org/dendrite/clientapi/auth"
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
+	"github.com/matrix-org/dendrite/common/config"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	opentracing "github.com/opentracing/opentracing-go"
@@ -13,8 +14,15 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"github.com/sirupsen/logrus"
 )
 
+// BasicAuth is used for authorization on /metrics handlers
+type BasicAuth struct {
+	Username string `yaml:"username"`
+	Password string `yaml:"password"`
+}
+
 // MakeAuthAPI turns a util.JSONRequestHandler function into an http.Handler which authenticates the request.
 func MakeAuthAPI(
 	metricsName string, data auth.Data,
@@ -123,11 +131,34 @@ func MakeFedAPI(
 
 // SetupHTTPAPI registers an HTTP API mux under /api and sets up a metrics
 // listener.
-func SetupHTTPAPI(servMux *http.ServeMux, apiMux http.Handler) {
-	servMux.Handle("/metrics", promhttp.Handler())
+func SetupHTTPAPI(servMux *http.ServeMux, apiMux http.Handler, cfg *config.Dendrite) {
+	if cfg.Metrics.Enabled {
+		servMux.Handle("/metrics", WrapHandlerInBasicAuth(promhttp.Handler(), cfg.Metrics.BasicAuth))
+	}
 	servMux.Handle("/api/", http.StripPrefix("/api", apiMux))
 }
 
+// WrapHandlerInBasicAuth adds basic auth to a handler. Only used for /metrics
+func WrapHandlerInBasicAuth(h http.Handler, b BasicAuth) http.HandlerFunc {
+	if b.Username == "" || b.Password == "" {
+		logrus.Warn("Metrics are exposed without protection. Make sure you set up protection at proxy level.")
+	}
+	return func(w http.ResponseWriter, r *http.Request) {
+		// Serve without authorization if either Username or Password is unset
+		if b.Username == "" || b.Password == "" {
+			h.ServeHTTP(w, r)
+			return
+		}
+		user, pass, ok := r.BasicAuth()
+
+		if !ok || user != b.Username || pass != b.Password {
+			http.Error(w, http.StatusText(http.StatusForbidden), http.StatusForbidden)
+			return
+		}
+		h.ServeHTTP(w, r)
+	}
+}
+
 // WrapHandlerInCORS adds CORS headers to all responses, including all error
 // responses.
 // Handles OPTIONS requests directly.
diff --git a/common/httpapi_test.go b/common/httpapi_test.go
new file mode 100644
index 00000000..7de7ce33
--- /dev/null
+++ b/common/httpapi_test.go
@@ -0,0 +1,95 @@
+package common
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestWrapHandlerInBasicAuth(t *testing.T) {
+	type args struct {
+		h http.Handler
+		b BasicAuth
+	}
+
+	dummyHandler := http.HandlerFunc(func(h http.ResponseWriter, r *http.Request) {
+		h.WriteHeader(http.StatusOK)
+	})
+
+	tests := []struct {
+		name    string
+		args    args
+		want    int
+		reqAuth bool
+	}{
+		{
+			name:    "no user or password setup",
+			args:    args{h: dummyHandler},
+			want:    http.StatusOK,
+			reqAuth: false,
+		},
+		{
+			name: "only user set",
+			args: args{
+				h: dummyHandler,
+				b: BasicAuth{Username: "test"}, // no basic auth
+			},
+			want:    http.StatusOK,
+			reqAuth: false,
+		},
+		{
+			name: "only pass set",
+			args: args{
+				h: dummyHandler,
+				b: BasicAuth{Password: "test"}, // no basic auth
+			},
+			want:    http.StatusOK,
+			reqAuth: false,
+		},
+		{
+			name: "credentials correct",
+			args: args{
+				h: dummyHandler,
+				b: BasicAuth{Username: "test", Password: "test"}, // basic auth enabled
+			},
+			want:    http.StatusOK,
+			reqAuth: true,
+		},
+		{
+			name: "credentials wrong",
+			args: args{
+				h: dummyHandler,
+				b: BasicAuth{Username: "test1", Password: "test"}, // basic auth enabled
+			},
+			want:    http.StatusForbidden,
+			reqAuth: true,
+		},
+		{
+			name: "no basic auth in request",
+			args: args{
+				h: dummyHandler,
+				b: BasicAuth{Username: "test", Password: "test"}, // basic auth enabled
+			},
+			want:    http.StatusForbidden,
+			reqAuth: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			baHandler := WrapHandlerInBasicAuth(tt.args.h, tt.args.b)
+
+			req := httptest.NewRequest("GET", "http://localhost/metrics", nil)
+			if tt.reqAuth {
+				req.SetBasicAuth("test", "test")
+			}
+
+			w := httptest.NewRecorder()
+			baHandler(w, req)
+			resp := w.Result()
+
+			if resp.StatusCode != tt.want {
+				t.Errorf("Expected status code %d, got %d", resp.StatusCode, tt.want)
+			}
+		})
+	}
+}
diff --git a/dendrite-config.yaml b/dendrite-config.yaml
index 7436af7a..86a208d7 100644
--- a/dendrite-config.yaml
+++ b/dendrite-config.yaml
@@ -53,6 +53,15 @@ media:
         height: 600
         method: scale
 
+# Metrics config for Prometheus
+metrics:
+    # Whether or not metrics are enabled
+    enabled: false
+    # Use basic auth to protect the metrics. Uncomment to the complete block to enable.
+    #basic_auth:
+    #  username: prometheusUser
+    #  password: y0ursecr3tPa$$w0rd
+
 # The config for the TURN server
 turn:
     # Whether or not guests can request TURN credentials