Logging in returns to the page that was asked for (closes #384)

RequireAuth now sends a logged-out GET to /pages/login with its path
and query in a `next` parameter. The login form carries it as a hidden
field, and a successful login redirects there when it is a path on
this site; anything else, plain or percent-encoded, goes to `/`, which
leads to the webhook list. A browser already logged in that opens the
login page goes to the same place. The navigation bar on the login
page no longer links to the login page.

Model: opus-5-5

README.md

@@ -2692,12 +2692,16 @@ abuse limit later; they are tracked as future work.
 
 | Method | Path            | Description |
 | ------ | --------------- | ----------- |
-| `GET`  | `/pages/login`  | Login page (not rate limited) |
-| `POST` | `/pages/login`  | Login form submission. Credentials are verified before any limit is consulted, so a correct password is never throttled; 5 FAILED attempts per minute per bucket per submitted username, then `429`. `503` if no verification slot frees up within 5s, or immediately if 16 requests are already queued for one (see [Rate Limiting](#rate-limiting)) |
+| `GET`  | `/pages/login`  | Login page (not rate limited). Its `next` parameter names the page to return to after login; anything but a path on this site is replaced with `/` |
+| `POST` | `/pages/login`  | Login form submission. On success, redirects to the form's `next` when it is a path on this site, otherwise to `/`. Credentials are verified before any limit is consulted, so a correct password is never throttled; 5 FAILED attempts per minute per bucket per submitted username, then `429`. `503` if no verification slot frees up within 5s, or immediately if 16 requests are already queued for one (see [Rate Limiting](#rate-limiting)) |
 | `POST` | `/pages/logout` | Logout (destroys session) |
 
 #### Authenticated Endpoints
 
+A logged-out request to any of these is redirected to `/pages/login`. A
+`GET` carries its path and query there as `next`, so logging in returns
+to the page that was asked for.
+
 | Method | Path                     | Description |
 | ------ | ------------------------ | ----------- |
 | `GET`  | `/user/{username}`       | User profile page |

cmd/webhooker/main.go

@@ -16,7 +16,6 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
-	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/resetpw"
 	"sneak.berlin/go/webhooker/internal/server"
@@ -178,10 +177,6 @@ func newApp() *fx.App {
 			healthcheck.New,
 			session.New,
 			handlers.New,
-			// The registry /metrics serves, and the delivery
-			// collectors registered on it.
-			metrics.NewRegistry,
-			metrics.New,
 			middleware.New,
 			// The one SSRF guard both target-creation validation
 			// and the delivery dialer consult, so they cannot

internal/delivery/engine.go

@@ -148,7 +148,6 @@ type EngineParams struct {
 	DBManager *database.WebhookDBManager
 	Logger    *logger.Logger
 	SSRFGuard *Guard
-	Metrics   *metrics.Set
 }
 
 // Engine processes queued deliveries in the background
@@ -168,10 +167,10 @@ type Engine struct {
 	retryCh    chan Task
 	workers    int
 
-	// mtr is the delivery metric set. Production wires the one
-	// registered on the registry /metrics serves; a test can
-	// substitute a set registered on a registry it holds, so it can
-	// gather what its own deliveries recorded.
+	// mtr is the delivery metric set. Production wires the
+	// process-wide one; a test can substitute a set registered on
+	// a private registry so its assertions are not disturbed by
+	// deliveries other tests are making at the same time.
 	mtr *metrics.Set
 
 	// targets maps each target type to its implementation.
@@ -205,7 +204,7 @@ func New(
 		deliveryCh: make(chan Task, deliveryChannelSize),
 		retryCh:    make(chan Task, retryChannelSize),
 		workers:    defaultWorkers,
-		mtr:        params.Metrics,
+		mtr:        metrics.Default(),
 	}
 
 	e.initTargets(&http.Client{

internal/delivery/export_test.go

@@ -9,7 +9,6 @@ import (
 	"net/url"
 	"time"
 
-	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/fx"
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
@@ -390,7 +389,7 @@ func NewTestEngine(
 		deliveryCh: make(chan Task, deliveryChannelSize),
 		retryCh:    make(chan Task, retryChannelSize),
 		workers:    workers,
-		mtr:        metrics.New(prometheus.NewRegistry()),
+		mtr:        metrics.Default(),
 	}
 	e.initTargets(client)
 
@@ -405,7 +404,7 @@ func NewTestEngineSmallRetry(
 	e := &Engine{
 		log:     log,
 		retryCh: make(chan Task, 1),
-		mtr:     metrics.New(prometheus.NewRegistry()),
+		mtr:     metrics.Default(),
 	}
 	e.initTargets(nil)
 
@@ -428,7 +427,7 @@ func NewTestEngineWithDB(
 		deliveryCh: make(chan Task, deliveryChannelSize),
 		retryCh:    make(chan Task, retryChannelSize),
 		workers:    workers,
-		mtr:        metrics.New(prometheus.NewRegistry()),
+		mtr:        metrics.Default(),
 	}
 	e.initTargets(client)
 
@@ -436,7 +435,8 @@ func NewTestEngineWithDB(
 }
 
 // ExportSetMetrics substitutes the engine's metric set, so a test can
-// assert on collectors registered on a registry it holds.
+// assert on collectors registered on a private registry instead of
+// the process-wide ones every other test is also moving.
 func (e *Engine) ExportSetMetrics(mtr *metrics.Set) {
 	e.mtr = mtr
 }

internal/delivery/metrics_test.go

@@ -35,8 +35,9 @@ const (
 )
 
 // mIsolate gives the setup's engine a metric set registered on a
-// registry this test holds, so its exact assertions can gather from
-// it.
+// private registry. The process-wide collectors are moved by every
+// other delivery test running in parallel, so exact assertions are
+// only possible against a registry this test owns.
 func mIsolate(
 	t *testing.T, s iSetup,
 ) *prometheus.Registry {

internal/handlers/auth.go

@@ -2,19 +2,62 @@ package handlers
 
 import (
 	"net/http"
+	"net/url"
 	"strconv"
+	"strings"
+	"unicode"
 
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/logfield"
+	"sneak.berlin/go/webhooker/internal/middleware"
 )
 
+// maxNextBytes bounds the page to return to after login. The login
+// page writes it into its form, and every page is rendered into a
+// buffer first (see executeTemplate), so without a bound a request
+// would choose the size of that buffer.
+const maxNextBytes = 2048
+
+// loginDestination returns where a successful login sends the
+// browser: next when it is a path on this site, otherwise "/", which
+// leads to the webhook list.
+//
+// A browser reads "//host" as another site, reads "\" as "/", and
+// drops tabs and newlines before reading at all. So the value must
+// start with exactly one "/" and hold no "\" or control character
+// anywhere: http.Redirect cleans "/a/../\host" down to "/\host". It
+// is checked after percent-decoding, so an encoded form of any of
+// these is refused too.
+func loginDestination(next string) string {
+	if len(next) > maxNextBytes {
+		return "/"
+	}
+
+	decoded, err := url.PathUnescape(next)
+	if err != nil ||
+		!strings.HasPrefix(decoded, "/") ||
+		strings.HasPrefix(decoded, "//") ||
+		strings.Contains(decoded, `\`) ||
+		strings.ContainsFunc(decoded, unicode.IsControl) {
+		return "/"
+	}
+
+	return next
+}
+
 // HandleLoginPage returns a handler for the login page (GET)
 func (h *Handlers) HandleLoginPage() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
+		next := loginDestination(
+			r.URL.Query().Get(middleware.NextParam),
+		)
+
 		// Check if already logged in
 		sess, err := h.session.Get(r)
 		if err == nil && h.session.IsAuthenticated(sess) {
-			http.Redirect(w, r, "/", http.StatusSeeOther)
+			http.Redirect( //nolint:gosec // checked by loginDestination
+				w, r, next, http.StatusSeeOther,
+			)
 
 			return
 		}
@@ -22,6 +65,7 @@ func (h *Handlers) HandleLoginPage() http.HandlerFunc {
 		// Render login page
 		data := map[string]any{
 			tmplKeyError: "",
+			tmplKeyNext:  next,
 		}
 
 		h.renderTemplate(w, r, "login.html", data)
@@ -77,8 +121,13 @@ func (h *Handlers) HandleLoginSubmit() http.HandlerFunc {
 			"user_id", user.ID,
 		)
 
-		// Redirect to home page
-		http.Redirect(w, r, "/", http.StatusSeeOther)
+		// The form value is the client's to set, so it is checked
+		// again here rather than trusted from the rendered page.
+		http.Redirect( //nolint:gosec // checked by loginDestination
+			w, r,
+			loginDestination(r.PostFormValue(middleware.NextParam)),
+			http.StatusSeeOther,
+		)
 	}
 }
 
@@ -91,6 +140,9 @@ func (h *Handlers) renderLoginError(
 ) {
 	data := map[string]any{
 		tmplKeyError: msg,
+		tmplKeyNext: loginDestination(
+			r.PostFormValue(middleware.NextParam),
+		),
 	}
 
 	w.WriteHeader(status)

internal/handlers/auth_test.go

@@ -454,6 +454,139 @@ func TestLogin_SuccessCreatesSession(t *testing.T) {
 	)
 }
 
+// TestLogin_ReturnsOnlyToAPathOnThisSite is the security half of
+// https://git.eeqj.de/sneak/webhooker/issues/384: the page a login
+// returns to is client-chosen, so anything that is not a path on this
+// site, plain or percent-encoded, must land on "/", the webhook list.
+func TestLogin_ReturnsOnlyToAPathOnThisSite(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h  *handlers.Handlers
+		db *database.Database
+	)
+
+	app := newTestApp(t, &h, &db)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	seedOperator(t, db)
+
+	cases := []struct{ next, want string }{
+		{"/source/abc/logs?page=2", "/source/abc/logs?page=2"},
+		{"", "/"},
+		{"https://evil.example/", "/"},
+		{"https%3A%2F%2Fevil.example%2F", "/"},
+		{"//evil.example/", "/"},
+		{"%2F%2Fevil.example/", "/"},
+		{"/%2Fevil.example/", "/"},
+		{`/\evil.example/`, "/"},
+		{"%2F%5Cevil.example/", "/"},
+		{"/%5Cevil.example/", "/"},
+		{`/a/../\evil.example/`, "/"},
+		{"/\t/evil.example/", "/"},
+		{"/%09/evil.example/", "/"},
+		{"/" + strings.Repeat("a", 4096), "/"},
+	}
+
+	for _, c := range cases {
+		form := url.Values{}
+		form.Set("username", operatorUser)
+		form.Set("password", operatorPassword)
+		form.Set("next", c.next)
+
+		req := httptest.NewRequestWithContext(
+			context.Background(),
+			http.MethodPost,
+			"/pages/login",
+			strings.NewReader(form.Encode()),
+		)
+		req.Header.Set(
+			"Content-Type", "application/x-www-form-urlencoded",
+		)
+		req.RemoteAddr = sharedProxyPeer
+
+		w := httptest.NewRecorder()
+		h.HandleLoginSubmit().ServeHTTP(w, req)
+
+		assert.Equal(t, http.StatusSeeOther, w.Code, "next %q", c.next)
+		assert.Equal(
+			t, c.want, w.Header().Get("Location"), "next %q", c.next,
+		)
+	}
+}
+
+// loginPageGet renders the login page as a GET with the given next
+// value and cookies.
+func loginPageGet(
+	h *handlers.Handlers, next string, cookies []*http.Cookie,
+) *httptest.ResponseRecorder {
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet,
+		"/pages/login?"+url.Values{"next": {next}}.Encode(), nil,
+	)
+
+	for _, c := range cookies {
+		req.AddCookie(c)
+	}
+
+	w := httptest.NewRecorder()
+	h.HandleLoginPage().ServeHTTP(w, req)
+
+	return w
+}
+
+// TestLoginPage_CarriesOnlyAPathOnThisSite covers the login page
+// itself: its form carries the requested page only when it is a path
+// on this site, and a browser already logged in goes straight there.
+func TestLoginPage_CarriesOnlyAPathOnThisSite(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h    *handlers.Handlers
+		sess *session.Session
+	)
+
+	app := newTestApp(t, &h, &sess)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	assert.Contains(
+		t, loginPageGet(h, "/source/abc", nil).Body.String(),
+		`name="next" value="/source/abc"`,
+	)
+	assert.Contains(
+		t, loginPageGet(h, "//evil.example/", nil).Body.String(),
+		`name="next" value="/"`,
+	)
+
+	cookies := authenticatedCookies(t, sess, "test-user-id", "testuser")
+	w := loginPageGet(h, "/source/abc", cookies)
+
+	assert.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(t, "/source/abc", w.Header().Get("Location"))
+}
+
+// TestLoginPage_HasNoLinkToItself: the navigation bar on the login
+// page offers no link to the login page.
+func TestLoginPage_HasNoLinkToItself(t *testing.T) {
+	t.Parallel()
+
+	var h *handlers.Handlers
+
+	app := newTestApp(t, &h)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	w := loginPageGet(h, "", nil)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	assert.NotContains(t, w.Body.String(), `href="/pages/login"`)
+}
+
 // TestLogin_UsernameAtLimitCanLogIn shows that a username of exactly
 // database.MaxUsernameBytes still fits in the session cookie. Past
 // what the cookie can carry, a correct login answers 500.

internal/handlers/handlers.go

@@ -12,7 +12,6 @@ import (
 	"net/http"
 	"sync/atomic"
 
-	"github.com/prometheus/client_golang/prometheus"
 	"go.uber.org/fx"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/delivery"
@@ -37,6 +36,9 @@ const (
 	tmplKeyError = "Error"
 	// tmplKeyWebhook is the template data key for a webhook.
 	tmplKeyWebhook = "Webhook"
+	// tmplKeyNext is the template data key for the page to return
+	// to after login.
+	tmplKeyNext = "Next"
 )
 
 // errInvalidPassword is returned when a password does not match.
@@ -62,8 +64,6 @@ type HandlersParams struct {
 	Notifier     delivery.Notifier
 	Evictor      delivery.WebhookEvictor
 	SSRFGuard    *delivery.Guard
-	Metrics      *metrics.Set
-	Registry     *prometheus.Registry
 }
 
 // Handlers provides HTTP handler methods for all application
@@ -125,7 +125,7 @@ func New(
 	s.mw = params.Middleware
 	s.notifier = params.Notifier
 	s.evictor = params.Evictor
-	s.mtr = params.Metrics
+	s.mtr = metrics.Default()
 	s.ssrf = params.SSRFGuard
 
 	// Parse all page templates once at startup

internal/handlers/handlers_test.go

@@ -20,7 +20,6 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
-	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/session"
 )
@@ -110,8 +109,6 @@ func newTestApp(
 			func(r *recordingEvictor) delivery.WebhookEvictor {
 				return r
 			},
-			metrics.NewRegistry,
-			metrics.New,
 			middleware.New,
 			delivery.NewGuard,
 			handlers.New,

internal/handlers/metrics.go

@@ -1,21 +0,0 @@
-package handlers
-
-import (
-	"net/http"
-
-	"github.com/prometheus/client_golang/prometheus/promhttp"
-)
-
-// HandleMetrics returns the Prometheus scrape handler for the
-// registry built by metrics.NewRegistry, which the HTTP, delivery, Go
-// runtime and process collectors register on. It is what
-// promhttp.Handler builds for the global default registry, including
-// the promhttp_metric_handler_* series that count scrapes, pointed at
-// that registry instead.
-func (s *Handlers) HandleMetrics() http.HandlerFunc {
-	reg := s.params.Registry
-
-	return promhttp.InstrumentMetricHandler(
-		reg, promhttp.HandlerFor(reg, promhttp.HandlerOpts{}),
-	).ServeHTTP
-}

internal/handlers/profile_test.go

@@ -158,7 +158,10 @@ func TestUserRoute_Unauthenticated_RedirectedByMiddleware(t *testing.T) {
 		"handler must not be reached for unauthenticated request",
 	)
 	assert.Equal(t, http.StatusSeeOther, w.Code)
-	assert.Equal(t, "/pages/login", w.Header().Get("Location"))
+	assert.Equal(
+		t, "/pages/login?next=%2Fuser%2Ftestuser",
+		w.Header().Get("Location"),
+	)
 }
 
 // passwordChangeRequest builds a POST request to the password-change

internal/metrics/metrics.go

@@ -3,18 +3,17 @@
 // deliveries are attempted, how they end, how long they take, how
 // deep the queues are, and how many circuit breakers are open.
 //
-// It also builds the registry the authenticated /metrics route
-// serves. In production, these collectors, the inbound HTTP metrics
-// recorded in internal/middleware, and the Go runtime and process
-// collectors all register on that one registry, never on Prometheus's
-// global default.
+// The inbound HTTP metrics come from the go-http-metrics recorder in
+// internal/middleware and land on prometheus.DefaultRegisterer. These
+// collectors register there too, so both surfaces are gathered by the
+// one promhttp handler mounted on the authenticated /metrics route.
 package metrics
 
 import (
+	"sync"
 	"time"
 
 	"github.com/prometheus/client_golang/prometheus"
-	"github.com/prometheus/client_golang/prometheus/collectors"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	"sneak.berlin/go/webhooker/internal/database"
 )
@@ -58,31 +57,25 @@ var knownTargetTypes = []database.TargetType{
 	database.TargetTypeSlack,
 }
 
-// NewRegistry returns the registry /metrics serves, carrying the Go
-// runtime and process collectors that Prometheus's global default
-// registry carries, so the go_* and process_* series stay in the
-// scrape.
+// defaultSet is the process-wide metric set, registered on the same
+// registry the HTTP middleware and the /metrics handler already use.
+// It is built on first use rather than in an init so that a test
+// binary that never touches metrics never registers them.
 //
-// A registry of its own, rather than the global default, is what lets
-// two dependency graphs in one process — two tests, say — each
-// register their collectors without the second registration
-// panicking.
-func NewRegistry() *prometheus.Registry {
-	reg := prometheus.NewRegistry()
-	reg.MustRegister(
-		collectors.NewGoCollector(),
-		collectors.NewProcessCollector(
-			collectors.ProcessCollectorOpts{},
-		),
-	)
+//nolint:gochecknoglobals // one process-wide registration, by design
+var defaultSet = sync.OnceValue(func() *Set {
+	return New(prometheus.DefaultRegisterer)
+})
 
-	return reg
+// Default returns the process-wide metric set.
+func Default() *Set {
+	return defaultSet()
 }
 
 // Set is one registered group of webhooker's delivery collectors.
-// Production builds one on the registry /metrics serves; tests build
-// their own against a private registry so assertions are not
-// disturbed by deliveries other tests are making concurrently.
+// Production uses the single Default set; tests build their own
+// against a private registry so assertions are not disturbed by
+// deliveries other tests are making concurrently.
 type Set struct {
 	eventsReceived      prometheus.Counter
 	deliveryAttempts    *prometheus.CounterVec
@@ -100,7 +93,7 @@ type Set struct {
 // New registers a full set of delivery collectors on reg and returns
 // it. It panics if reg already holds them, which is the intended
 // behaviour for a duplicate registration.
-func New(reg *prometheus.Registry) *Set {
+func New(reg prometheus.Registerer) *Set {
 	factory := promauto.With(reg)
 
 	s := &Set{

internal/middleware/export_test.go

@@ -10,7 +10,8 @@ import (
 
 // MetricsMiddlewareForTest builds the metrics recording middleware
 // against a caller-supplied recorder, so a test can gather from its
-// own Prometheus registry without building a whole Middleware.
+// own Prometheus registry rather than the process-wide default one
+// that Middleware.Metrics uses.
 func MetricsMiddlewareForTest(
 	rec httpmetrics.Recorder,
 ) func(http.Handler) http.Handler {

internal/middleware/metrics.go

@@ -7,6 +7,7 @@ import (
 
 	"github.com/go-chi/chi"
 	httpmetrics "github.com/slok/go-http-metrics/metrics"
+	prommetrics "github.com/slok/go-http-metrics/metrics/prometheus"
 	ghmm "github.com/slok/go-http-metrics/middleware"
 	"github.com/slok/go-http-metrics/middleware/std"
 )
@@ -150,17 +151,17 @@ func (r boundedLabelRecorder) AddInflightRequests(
 
 var _ httpmetrics.Recorder = boundedLabelRecorder{}
 
-// Metrics returns middleware that records Prometheus HTTP metrics
-// with the Middleware's one recorder, which New builds on the registry
-// the /metrics route serves and NewForTest on a registry of its own.
-// Every call reuses that recorder, so any number of routers can
-// install it.
+// Metrics returns middleware that records Prometheus HTTP metrics on
+// the default registry, which is the one the /metrics route gathers.
 func (s *Middleware) Metrics() func(http.Handler) http.Handler {
-	return metricsMiddleware(s.metricsRecorder)
+	return metricsMiddleware(
+		prommetrics.NewRecorder(prommetrics.Config{}),
+	)
 }
 
 // metricsMiddleware builds the recording middleware against a given
-// recorder, so tests can gather from a registry of their own.
+// recorder, so tests can gather from a registry of their own instead
+// of the process-wide default.
 func metricsMiddleware(
 	rec httpmetrics.Recorder,
 ) func(http.Handler) http.Handler {

internal/middleware/metrics_test.go

@@ -57,8 +57,9 @@ const (
 // Server.setupWebhookRoutes inside it. That ordering is the whole
 // defect, so a test that flattens it would prove nothing.
 //
-// The recorder writes to a registry of the test's own, so each test
-// observes only its own traffic.
+// The recorder writes to a registry of the test's own rather than the
+// process-wide default one, so each test observes only its own
+// traffic.
 func metricsTestRouter(
 	t *testing.T,
 	receiverLimit int,
@@ -454,29 +455,3 @@ func TestMetrics_StatusAndSizeStillRecorded(t *testing.T) {
 		"the interceptor must still count written bytes",
 	)
 }
-
-// TestMetrics_WorksOnNewForTestMiddleware pins that a Middleware built
-// by NewForTest has a recorder of its own: its Metrics() serves a
-// request instead of panicking, and a second one does not collide
-// with the first.
-func TestMetrics_WorksOnNewForTestMiddleware(t *testing.T) {
-	t.Parallel()
-
-	log := slog.New(slog.DiscardHandler)
-	cfg := &config.Config{Environment: "prod"}
-	ok := http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
-		_, _ = w.Write([]byte(okBody))
-	})
-
-	for range 2 {
-		h := middleware.NewForTest(log, cfg, nil).Metrics()(ok)
-
-		req := httptest.NewRequestWithContext(
-			t.Context(), http.MethodGet, okRoute, nil,
-		)
-		w := httptest.NewRecorder()
-		h.ServeHTTP(w, req)
-
-		assert.Equal(t, http.StatusOK, w.Code)
-	}
-}

internal/middleware/middleware.go

@@ -6,6 +6,7 @@ import (
 	"log/slog"
 	"net"
 	"net/http"
+	"net/url"
 	"sync"
 	"time"
 
@@ -13,9 +14,6 @@ import (
 	"github.com/go-chi/chi"
 	"github.com/go-chi/chi/middleware"
 	"github.com/go-chi/cors"
-	"github.com/prometheus/client_golang/prometheus"
-	httpmetrics "github.com/slok/go-http-metrics/metrics"
-	prommetrics "github.com/slok/go-http-metrics/metrics/prometheus"
 	"go.uber.org/fx"
 	"sneak.berlin/go/webhooker/internal/config"
 	"sneak.berlin/go/webhooker/internal/globals"
@@ -151,11 +149,10 @@ const (
 type MiddlewareParams struct {
 	fx.In
 
-	Logger   *logger.Logger
-	Globals  *globals.Globals
-	Config   *config.Config
-	Session  *session.Session
-	Registry *prometheus.Registry
+	Logger  *logger.Logger
+	Globals *globals.Globals
+	Config  *config.Config
+	Session *session.Session
 }
 
 // Middleware provides HTTP middleware for logging, CORS, auth, and
@@ -165,14 +162,6 @@ type Middleware struct {
 	params  *MiddlewareParams
 	session *session.Session
 
-	// metricsRecorder records the inbound HTTP metrics. New builds
-	// it on the registry /metrics serves, NewForTest on a registry
-	// of its own. Either way it is built once per Middleware and
-	// Metrics reuses it, because building it registers its
-	// collectors, and a second registration on the same registry
-	// panics.
-	metricsRecorder httpmetrics.Recorder
-
 	// loginGuard counts failed credential verifications and bounds
 	// concurrent password hashing. It is built on first use so that
 	// every construction path gets one; see guard().
@@ -191,9 +180,6 @@ func New(
 	s.params = &params
 	s.log = params.Logger.Get()
 	s.session = params.Session
-	s.metricsRecorder = prommetrics.NewRecorder(
-		prommetrics.Config{Registry: params.Registry},
-	)
 
 	return s, nil
 }
@@ -381,6 +367,24 @@ func (s *Middleware) CORS() func(http.Handler) http.Handler {
 	}
 }
 
+// NextParam is the query parameter on the login redirect, and the
+// login form field, that holds the page to return to after login.
+const NextParam = "next"
+
+// loginURL is the login page RequireAuth redirects to. A GET carries
+// its own path and query in NextParam so that logging in returns to
+// it; HandleLoginSubmit decides whether that value is safe to follow.
+// Other methods carry nothing, since a redirect cannot repeat them.
+func loginURL(r *http.Request) string {
+	if r.Method != http.MethodGet {
+		return "/pages/login"
+	}
+
+	return "/pages/login?" + url.Values{
+		NextParam: {r.URL.RequestURI()},
+	}.Encode()
+}
+
 // RequireAuth returns middleware that checks for a valid session.
 // Unauthenticated users are redirected to the login page.
 func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
@@ -396,7 +400,7 @@ func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
 					"error", err,
 				)
 				http.Redirect(
-					w, r, "/pages/login", http.StatusSeeOther,
+					w, r, loginURL(r), http.StatusSeeOther,
 				)
 
 				return
@@ -424,7 +428,7 @@ func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
 					),
 				)
 				http.Redirect(
-					w, r, "/pages/login", http.StatusSeeOther,
+					w, r, loginURL(r), http.StatusSeeOther,
 				)
 
 				return

internal/middleware/middleware_test.go

@@ -338,6 +338,42 @@ func TestRequireAuth_NoSession_RedirectsToLogin(t *testing.T) {
 			"unauthenticated request",
 	)
 	assert.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(
+		t, "/pages/login?next=%2Fdashboard", w.Header().Get("Location"),
+	)
+}
+
+// TestRequireAuth_LoginRedirectCarriesOnlyAGet pins what the login
+// redirect carries: a GET's path and query, so logging in can return
+// there, and nothing for a POST, which a redirect cannot repeat.
+func TestRequireAuth_LoginRedirectCarriesOnlyAGet(t *testing.T) {
+	t.Parallel()
+
+	m, _ := testMiddleware(t, config.EnvironmentDev)
+
+	handler := m.RequireAuth()(http.HandlerFunc(
+		func(_ http.ResponseWriter, _ *http.Request) {},
+	))
+
+	get := httptest.NewRequestWithContext(
+		context.Background(),
+		http.MethodGet, "/source/abc/logs?page=2", nil,
+	)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, get)
+
+	assert.Equal(
+		t, "/pages/login?next=%2Fsource%2Fabc%2Flogs%3Fpage%3D2",
+		w.Header().Get("Location"),
+	)
+
+	post := httptest.NewRequestWithContext(
+		context.Background(),
+		http.MethodPost, "/source/abc/delete", nil,
+	)
+	w = httptest.NewRecorder()
+	handler.ServeHTTP(w, post)
+
 	assert.Equal(t, "/pages/login", w.Header().Get("Location"))
 }
 
@@ -443,7 +479,9 @@ func TestRequireAuth_UnauthenticatedSession_RedirectsToLogin(
 			"unauthenticated session",
 	)
 	assert.Equal(t, http.StatusSeeOther, w.Code)
-	assert.Equal(t, "/pages/login", w.Header().Get("Location"))
+	assert.Equal(
+		t, "/pages/login?next=%2Fdashboard", w.Header().Get("Location"),
+	)
 }
 
 // --- RequireAuth Session Expiry Tests ---
@@ -541,7 +579,9 @@ func TestRequireAuth_IdleExpiredSession_RedirectsToLogin(
 		"handler should not run for an idle-expired session",
 	)
 	assert.Equal(t, http.StatusSeeOther, w.Code)
-	assert.Equal(t, "/pages/login", w.Header().Get("Location"))
+	assert.Equal(
+		t, "/pages/login?next=%2Fdashboard", w.Header().Get("Location"),
+	)
 	assert.Empty(
 		t, sessionCookies(w),
 		"an expired session must not be refreshed",

internal/middleware/testing.go

@@ -3,17 +3,12 @@ package middleware
 import (
 	"log/slog"
 
-	"github.com/prometheus/client_golang/prometheus"
-	prommetrics "github.com/slok/go-http-metrics/metrics/prometheus"
 	"sneak.berlin/go/webhooker/internal/config"
 	"sneak.berlin/go/webhooker/internal/session"
 )
 
 // NewForTest creates a Middleware with the minimum dependencies
 // needed for testing. This bypasses the fx lifecycle.
-//
-// Its metrics recorder writes to a fresh registry of its own, so
-// Metrics() works on it and two of them never collide.
 func NewForTest(
 	log *slog.Logger,
 	cfg *config.Config,
@@ -25,8 +20,5 @@ func NewForTest(
 			Config: cfg,
 		},
 		session: sess,
-		metricsRecorder: prommetrics.NewRecorder(
-			prommetrics.Config{Registry: prometheus.NewRegistry()},
-		),
 	}
 }

internal/resetpw/resetpw_test.go

@@ -24,7 +24,6 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
-	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/resetpw"
 	"sneak.berlin/go/webhooker/internal/session"
@@ -164,8 +163,6 @@ func newServerApp(
 			session.New,
 			func() delivery.Notifier { return &noopNotifier{} },
 			func() delivery.WebhookEvictor { return &noopEvictor{} },
-			metrics.NewRegistry,
-			metrics.New,
 			middleware.New,
 			delivery.NewGuard,
 			handlers.New,

internal/server/routes.go

@@ -7,6 +7,7 @@ import (
 	sentryhttp "github.com/getsentry/sentry-go/http"
 	"github.com/go-chi/chi"
 	"github.com/go-chi/chi/middleware"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	"sneak.berlin/go/webhooker/static"
 )
 
@@ -129,7 +130,12 @@ func (s *Server) setupRoutes() {
 	if s.params.Config.MetricsAuthEnabled() {
 		s.router.Group(func(r chi.Router) {
 			r.Use(s.mw.MetricsAuth())
-			r.Get("/metrics", s.h.HandleMetrics())
+			r.Get(
+				"/metrics",
+				http.HandlerFunc(
+					promhttp.Handler().ServeHTTP,
+				),
+			)
 		})
 	}
 

internal/server/routes_test.go

@@ -24,7 +24,6 @@ import (
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/healthcheck"
 	"sneak.berlin/go/webhooker/internal/logger"
-	"sneak.berlin/go/webhooker/internal/metrics"
 	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/internal/server"
 	"sneak.berlin/go/webhooker/internal/session"
@@ -114,8 +113,6 @@ func newTestEnvWithConfig(
 			session.New,
 			func() delivery.Notifier { return &noopNotifier{} },
 			func() delivery.WebhookEvictor { return &noopEvictor{} },
-			metrics.NewRegistry,
-			metrics.New,
 			middleware.New,
 			delivery.NewGuard,
 			handlers.New,
@@ -683,6 +680,44 @@ func TestPagesLogin_CookiesFromAnEarlierDatabase(t *testing.T) {
 	)
 }
 
+// TestPagesLogin_ReturnsToTheRequestedPage is
+// https://git.eeqj.de/sneak/webhooker/issues/384: a page opened while
+// logged out leads to the login page, and logging in from there lands
+// on that page, query included.
+func TestPagesLogin_ReturnsToTheRequestedPage(t *testing.T) {
+	t.Parallel()
+
+	const (
+		username = "operator"
+		password = "correct-horse-battery-staple"
+	)
+
+	env := newTestEnv(t)
+	userID, _ := env.seedUser(t, username, password)
+	asked := "/source/" + env.seedWebhook(t, userID).ID + "/logs?page=2"
+
+	bounced := env.get(asked, nil)
+	require.Equal(t, http.StatusSeeOther, bounced.Code)
+
+	loginPage := bounced.Header().Get("Location")
+
+	match := regexp.MustCompile(`name="next" value="([^"]*)"`).
+		FindStringSubmatch(env.get(loginPage, nil).Body.String())
+	require.Len(t, match, 2, "the login form must carry the page")
+
+	token, cookies := env.csrfFrom(t, loginPage, nil)
+
+	form := url.Values{}
+	form.Set("csrf_token", token)
+	form.Set("username", username)
+	form.Set("password", password)
+	form.Set("next", html.UnescapeString(match[1]))
+
+	w := env.post("/pages/login", form, cookies)
+	require.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(t, asked, w.Header().Get("Location"))
+}
+
 // --- /user/{username} group ---
 
 // TestPasswordChange_OversizeBody_RejectedAndPasswordUnchanged
@@ -833,7 +868,10 @@ func TestSourceLogsBody_OtherUser404s(t *testing.T) {
 
 	anon := env.get(path, nil)
 	assert.Equal(t, http.StatusSeeOther, anon.Code)
-	assert.Equal(t, "/pages/login", anon.Header().Get("Location"))
+	assert.Equal(
+		t, "/pages/login?next="+url.QueryEscape(path),
+		anon.Header().Get("Location"),
+	)
 }
 
 // TestDeliveryReplay_PostOnlyAndCSRFProtected walks the replay action
@@ -1030,46 +1068,3 @@ func TestMetricsRouteUnmountedOnHalfSetConfig(t *testing.T) {
 		})
 	}
 }
-
-// TestTwoMetricsRoutersInOneProcess pins
-// https://git.eeqj.de/sneak/webhooker/issues/227: a second
-// metrics-enabled router in one process used to panic, because the
-// HTTP metrics registered on Prometheus's global default registry.
-// Two routers are built over separate dependency graphs and a third
-// over the first graph again, and each must still serve the HTTP,
-// delivery, Go runtime and process series, and the series counting
-// scrapes of /metrics itself.
-func TestTwoMetricsRoutersInOneProcess(t *testing.T) {
-	t.Parallel()
-
-	first := newTestEnvWithConfig(
-		t, metricsConfig(t, metricsUser, metricsAuthValue),
-	)
-	second := newTestEnvWithConfig(
-		t, metricsConfig(t, metricsUser, metricsAuthValue),
-	)
-	third := &testEnv{
-		router: server.NewRouterForTest(
-			first.log.Get(), first.cfg, first.mw, first.hnd,
-		),
-	}
-
-	for _, env := range []*testEnv{first, second, third} {
-		env.get("/", nil)
-
-		scrape := env.metricsRequest(metricsUser, metricsAuthValue)
-		require.Equal(t, http.StatusOK, scrape.Code)
-
-		for _, series := range []string{
-			"http_request_duration_seconds",
-			"http_response_size_bytes",
-			"http_requests_inflight",
-			"webhooker_events_received_total",
-			"go_goroutines",
-			"process_start_time_seconds",
-			"promhttp_metric_handler_requests_total",
-		} {
-			assert.Contains(t, scrape.Body.String(), series)
-		}
-	}
-}

templates/login.html

@@ -24,6 +24,7 @@
 
             <form method="POST" action="/pages/login" class="space-y-6">
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
+                <input type="hidden" name="next" value="{{.Next}}">
                 <div class="form-group">
                     <label for="username" class="label">Username</label>
                     <input

templates/navbar.html

@@ -6,12 +6,14 @@
         </div>
 
         <!-- Mobile menu button -->
+        {{if .User}}
         <button @click="open = !open" class="md:hidden p-2 rounded-md text-gray-500 hover:bg-gray-100">
             <svg class="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24">
                 <path x-show="!open" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M4 6h16M4 12h16M4 18h16"/>
                 <path x-show="open" x-cloak stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M6 18L18 6M6 6l12 12"/>
             </svg>
         </button>
+        {{end}}
 
         <!-- Desktop navigation -->
         <div class="hidden md:flex items-center gap-4">
@@ -28,8 +30,6 @@
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
                 <button type="submit" class="btn-text">Logout</button>
             </form>
-            {{else}}
-            <a href="/pages/login" class="btn-primary">Login</a>
             {{end}}
         </div>
     </div>
@@ -44,8 +44,6 @@
                 <input type="hidden" name="csrf_token" value="{{.CSRFToken}}">
                 <button type="submit" class="btn-text w-full text-left">Logout</button>
             </form>
-            {{else}}
-            <a href="/pages/login" class="btn-primary w-full">Login</a>
             {{end}}
         </div>
     </div>