docs(admin/policies): give people a python command

Signed-off-by: Xe Iaso <me@xeiaso.net>

.github/actions/spelling/allow.txt

@@ -38,3 +38,4 @@ Samsung
 wenet
 qwertiko
 setuplistener
+mba

data/botPolicies.yaml

@@ -175,6 +175,13 @@ status_codes:
 #   bind: ":9090"
 #   network: "tcp"
 #
+# # To protect your metrics server with basic auth, set credentials below:
+# #
+# # https://anubis.techaro.lol/docs/admin/policies#http-basic-authentication
+#   basicAuth:
+#     username: ""
+#     password: ""
+#
 # # To serve metrics over TLS, set the path to the right TLS certificate and key
 # # here. When the files change on disk, they will automatically be reloaded.
 # #

docs/docs/CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add Bulgarian locale ([#1394](https://github.com/TecharoHQ/anubis/pull/1394))
 - Fix CEL internal errors when iterating `headers`/`query` map wrappers by implementing map iterators for `HTTPHeaders` and `URLValues` ([#1465](https://github.com/TecharoHQ/anubis/pull/1465)).
 - Enable [metrics serving via TLS](./admin/policies.mdx#tls), including [mutual TLS (mTLS)](./admin/policies.mdx#mtls).
+- Enable [HTTP basic auth](./admin/policies.mdx#http-basic-authentication) for the metrics server.
 
 ## v1.25.0: Necron
 

docs/docs/admin/policies.mdx

@@ -171,6 +171,24 @@ metrics:
 
 As it is not expected for certificate authority certificates to change often, the CA certificate will NOT be automatically reloaded when the respective file changes.
 
+### HTTP basic authentication
+
+Anubis' metrics server also supports setting HTTP basic auth as a lightweight protection against unauthorized users viewing metrics data. As the basic auth credentials are hardcoded in the configuration file, administrators SHOULD use randomly generated credentials, such as type-4 UUIDs or other high entropy strings. These credentials MUST NOT be sensitive or used to protect other high value systems.
+
+Configure it with the `basicAuth` block under `metrics`:
+
+```yaml
+metrics:
+  bind: ":9090"
+  network: "tcp"
+
+  basicAuth:
+    username: azurediamond
+    password: hunter2
+```
+
+If you have Python installed, you can generate a high entropy password with `python -c 'import secrets; print(secrets.token_urlsafe(32))'`.
+
 ## Imprint / Impressum support
 
 Anubis has support for showing imprint / impressum information. This is defined in the `impressum` block of your configuration. See [Imprint / Impressum configuration](./configuration/impressum.mdx) for more information.

internal/basicauth.go

@@ -0,0 +1,52 @@
+package internal
+
+import (
+	"crypto/sha256"
+	"crypto/subtle"
+	"fmt"
+	"log/slog"
+	"net/http"
+)
+
+// BasicAuth wraps next in HTTP Basic authentication using the provided
+// credentials. If either username or password is empty, next is returned
+// unchanged and a debug log line is emitted.
+//
+// Credentials are compared in constant time to avoid leaking information
+// through timing side channels.
+func BasicAuth(realm, username, password string, next http.Handler) http.Handler {
+	if username == "" || password == "" {
+		slog.Debug("skipping middleware, basic auth credentials are empty")
+		return next
+	}
+
+	expectedUser := sha256.Sum256([]byte(username))
+	expectedPass := sha256.Sum256([]byte(password))
+	challenge := fmt.Sprintf("Basic realm=%q, charset=\"UTF-8\"", realm)
+
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		user, pass, ok := r.BasicAuth()
+		if !ok {
+			unauthorized(w, challenge)
+			return
+		}
+
+		gotUser := sha256.Sum256([]byte(user))
+		gotPass := sha256.Sum256([]byte(pass))
+
+		userMatch := subtle.ConstantTimeCompare(gotUser[:], expectedUser[:])
+		passMatch := subtle.ConstantTimeCompare(gotPass[:], expectedPass[:])
+
+		if userMatch&passMatch != 1 {
+			unauthorized(w, challenge)
+			return
+		}
+
+		next.ServeHTTP(w, r)
+	})
+}
+
+func unauthorized(w http.ResponseWriter, challenge string) {
+	w.Header().Set("WWW-Authenticate", challenge)
+	http.Error(w, "Unauthorized", http.StatusUnauthorized)
+}

internal/basicauth_test.go

@@ -0,0 +1,138 @@
+package internal
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func okHandler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+		_, _ = w.Write([]byte("ok"))
+	})
+}
+
+func TestBasicAuth(t *testing.T) {
+	t.Parallel()
+
+	const (
+		realm    = "test-realm"
+		username = "admin"
+		password = "hunter2"
+	)
+
+	for _, tt := range []struct {
+		name       string
+		setAuth    bool
+		user       string
+		pass       string
+		wantStatus int
+		wantBody   string
+		wantChall  bool
+	}{
+		{
+			name:       "valid credentials",
+			setAuth:    true,
+			user:       username,
+			pass:       password,
+			wantStatus: http.StatusOK,
+			wantBody:   "ok",
+		},
+		{
+			name:       "missing credentials",
+			setAuth:    false,
+			wantStatus: http.StatusUnauthorized,
+			wantChall:  true,
+		},
+		{
+			name:       "wrong username",
+			setAuth:    true,
+			user:       "nobody",
+			pass:       password,
+			wantStatus: http.StatusUnauthorized,
+			wantChall:  true,
+		},
+		{
+			name:       "wrong password",
+			setAuth:    true,
+			user:       username,
+			pass:       "wrong",
+			wantStatus: http.StatusUnauthorized,
+			wantChall:  true,
+		},
+		{
+			name:       "empty supplied credentials",
+			setAuth:    true,
+			user:       "",
+			pass:       "",
+			wantStatus: http.StatusUnauthorized,
+			wantChall:  true,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			h := BasicAuth(realm, username, password, okHandler())
+
+			req := httptest.NewRequest(http.MethodGet, "/", nil)
+			if tt.setAuth {
+				req.SetBasicAuth(tt.user, tt.pass)
+			}
+			rec := httptest.NewRecorder()
+			h.ServeHTTP(rec, req)
+
+			if rec.Code != tt.wantStatus {
+				t.Errorf("status = %d, want %d", rec.Code, tt.wantStatus)
+			}
+
+			if tt.wantBody != "" && rec.Body.String() != tt.wantBody {
+				t.Errorf("body = %q, want %q", rec.Body.String(), tt.wantBody)
+			}
+
+			chall := rec.Header().Get("WWW-Authenticate")
+			if tt.wantChall {
+				if chall == "" {
+					t.Error("WWW-Authenticate header missing on 401")
+				}
+				if !strings.Contains(chall, realm) {
+					t.Errorf("WWW-Authenticate = %q, want realm %q", chall, realm)
+				}
+			} else if chall != "" {
+				t.Errorf("unexpected WWW-Authenticate header: %q", chall)
+			}
+		})
+	}
+}
+
+func TestBasicAuthPassthrough(t *testing.T) {
+	t.Parallel()
+
+	for _, tt := range []struct {
+		name     string
+		username string
+		password string
+	}{
+		{name: "empty username", username: "", password: "hunter2"},
+		{name: "empty password", username: "admin", password: ""},
+		{name: "both empty", username: "", password: ""},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			h := BasicAuth("realm", tt.username, tt.password, okHandler())
+
+			req := httptest.NewRequest(http.MethodGet, "/", nil)
+			rec := httptest.NewRecorder()
+			h.ServeHTTP(rec, req)
+
+			if rec.Code != http.StatusOK {
+				t.Errorf("status = %d, want %d (passthrough expected)", rec.Code, http.StatusOK)
+			}
+			if rec.Body.String() != "ok" {
+				t.Errorf("body = %q, want %q", rec.Body.String(), "ok")
+			}
+		})
+	}
+}

lib/config/metrics.go

@@ -10,25 +10,29 @@ import (
 )
 
 var (
-	ErrInvalidMetricsConfig        = errors.New("config: invalid metrics configuration")
-	ErrInvalidMetricsTLSConfig     = errors.New("config: invalid metrics TLS configuration")
-	ErrNoMetricsBind               = errors.New("config.Metrics: must define bind")
-	ErrNoMetricsNetwork            = errors.New("config.Metrics: must define network")
-	ErrNoMetricsSocketMode         = errors.New("config.Metrics: must define socket mode when using unix sockets")
-	ErrInvalidMetricsSocketMode    = errors.New("config.Metrics: invalid unix socket mode")
-	ErrInvalidMetricsNetwork       = errors.New("config.Metrics: invalid metrics network")
-	ErrNoMetricsTLSCertificate     = errors.New("config.Metrics.TLS: must define certificate file")
-	ErrNoMetricsTLSKey             = errors.New("config.Metrics.TLS: must define key file")
-	ErrInvalidMetricsTLSKeypair    = errors.New("config.Metrics.TLS: keypair is invalid")
-	ErrInvalidMetricsCACertificate = errors.New("config.Metrics.TLS: invalid CA certificate")
-	ErrCantReadFile                = errors.New("config: can't read required file")
+	ErrInvalidMetricsConfig          = errors.New("config: invalid metrics configuration")
+	ErrInvalidMetricsTLSConfig       = errors.New("config: invalid metrics TLS configuration")
+	ErrInvalidMetricsBasicAuthConfig = errors.New("config: invalid metrics basic auth configuration")
+	ErrNoMetricsBind                 = errors.New("config.Metrics: must define bind")
+	ErrNoMetricsNetwork              = errors.New("config.Metrics: must define network")
+	ErrNoMetricsSocketMode           = errors.New("config.Metrics: must define socket mode when using unix sockets")
+	ErrInvalidMetricsSocketMode      = errors.New("config.Metrics: invalid unix socket mode")
+	ErrInvalidMetricsNetwork         = errors.New("config.Metrics: invalid metrics network")
+	ErrNoMetricsTLSCertificate       = errors.New("config.Metrics.TLS: must define certificate file")
+	ErrNoMetricsTLSKey               = errors.New("config.Metrics.TLS: must define key file")
+	ErrInvalidMetricsTLSKeypair      = errors.New("config.Metrics.TLS: keypair is invalid")
+	ErrInvalidMetricsCACertificate   = errors.New("config.Metrics.TLS: invalid CA certificate")
+	ErrCantReadFile                  = errors.New("config: can't read required file")
+	ErrNoMetricsBasicAuthUsername    = errors.New("config.Metrics.BasicAuth: must define username")
+	ErrNoMetricsBasicAuthPassword    = errors.New("config.Metrics.BasicAuth: must define password")
 )
 
 type Metrics struct {
-	Bind       string      `json:"bind" yaml:"bind"`
-	Network    string      `json:"network" yaml:"network"`
-	SocketMode string      `json:"socketMode" yaml:"socketMode"`
-	TLS        *MetricsTLS `json:"tls" yaml:"tls"`
+	Bind       string            `json:"bind" yaml:"bind"`
+	Network    string            `json:"network" yaml:"network"`
+	SocketMode string            `json:"socketMode" yaml:"socketMode"`
+	TLS        *MetricsTLS       `json:"tls" yaml:"tls"`
+	BasicAuth  *MetricsBasicAuth `json:"basicAuth" yaml:"basicAuth"`
 }
 
 func (m *Metrics) Valid() error {
@@ -62,6 +66,12 @@ func (m *Metrics) Valid() error {
 		}
 	}
 
+	if m.BasicAuth != nil {
+		if err := m.BasicAuth.Valid(); err != nil {
+			errs = append(errs, err)
+		}
+	}
+
 	if len(errs) != 0 {
 		return errors.Join(ErrInvalidMetricsConfig, errors.Join(errs...))
 	}
@@ -131,3 +141,26 @@ func canReadFile(fname string) error {
 
 	return nil
 }
+
+type MetricsBasicAuth struct {
+	Username string `json:"username" yaml:"username"`
+	Password string `json:"password" yaml:"password"`
+}
+
+func (mba *MetricsBasicAuth) Valid() error {
+	var errs []error
+
+	if mba.Username == "" {
+		errs = append(errs, ErrNoMetricsBasicAuthUsername)
+	}
+
+	if mba.Password == "" {
+		errs = append(errs, ErrNoMetricsBasicAuthPassword)
+	}
+
+	if len(errs) != 0 {
+		return errors.Join(ErrInvalidMetricsBasicAuthConfig, errors.Join(errs...))
+	}
+
+	return nil
+}

lib/config/metrics_test.go

@@ -157,6 +157,79 @@ func TestMetricsValid(t *testing.T) {
 			},
 			err: ErrInvalidMetricsCACertificate,
 		},
+		{
+			name: "basic auth credentials set",
+			input: &Metrics{
+				Bind:    ":9090",
+				Network: "tcp",
+				BasicAuth: &MetricsBasicAuth{
+					Username: "admin",
+					Password: "hunter2",
+				},
+			},
+		},
+		{
+			name: "invalid basic auth config",
+			input: &Metrics{
+				Bind:      ":9090",
+				Network:   "tcp",
+				BasicAuth: &MetricsBasicAuth{},
+			},
+			err: ErrInvalidMetricsBasicAuthConfig,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := tt.input.Valid(); !errors.Is(err, tt.err) {
+				t.Logf("wanted error: %v", tt.err)
+				t.Logf("got error:    %v", err)
+				t.Error("validation failed")
+			}
+		})
+	}
+}
+
+func TestMetricsBasicAuthValid(t *testing.T) {
+	for _, tt := range []struct {
+		name  string
+		input *MetricsBasicAuth
+		err   error
+	}{
+		{
+			name: "both set",
+			input: &MetricsBasicAuth{
+				Username: "admin",
+				Password: "hunter2",
+			},
+		},
+		{
+			name:  "empty username and password",
+			input: &MetricsBasicAuth{},
+			err:   ErrInvalidMetricsBasicAuthConfig,
+		},
+		{
+			name: "missing username",
+			input: &MetricsBasicAuth{
+				Password: "hunter2",
+			},
+			err: ErrNoMetricsBasicAuthUsername,
+		},
+		{
+			name: "missing password",
+			input: &MetricsBasicAuth{
+				Username: "admin",
+			},
+			err: ErrNoMetricsBasicAuthPassword,
+		},
+		{
+			name:  "missing both surfaces wrapper error",
+			input: &MetricsBasicAuth{},
+			err:   ErrNoMetricsBasicAuthUsername,
+		},
+		{
+			name:  "missing both surfaces password error",
+			input: &MetricsBasicAuth{},
+			err:   ErrNoMetricsBasicAuthPassword,
+		},
 	} {
 		t.Run(tt.name, func(t *testing.T) {
 			if err := tt.input.Valid(); !errors.Is(err, tt.err) {

lib/metrics/metrics.go

@@ -97,6 +97,13 @@ func (s *Server) run(ctx context.Context, lg *slog.Logger) error {
 		}
 	}
 
+	if s.Config.BasicAuth != nil {
+		var h http.Handler = mux
+		h = internal.BasicAuth("anubis-metrics", s.Config.BasicAuth.Username, s.Config.BasicAuth.Password, mux)
+
+		srv.Handler = h
+	}
+
 	lg.Debug("listening for metrics", "url", metricsURL)
 
 	go func() {