pixa/internal/server/login_rate_limit_internal_test.go

package server

import (
	"io"
	"net/http"
	"net/http/httptest"
	"net/netip"
	"net/url"
	"path/filepath"
	"regexp"
	"strconv"
	"strings"
	"testing"

	"sneak.berlin/go/pixa/internal/config"
)

// testSigningKey is a throwaway signing key; submitting it logs in.
const testSigningKey = "test-signing-key-0123456789abcdef"

// wrongKey is submitted for a failed login.
const wrongKey = "not-the-signing-key"

// Addresses for the login rate limit tests. The test server trusts
// 10.0.0.0/8 as its proxies, so the X-Forwarded-For sent by proxyPeer is
// believed and the one sent by firstClient or secondClient is ignored.
const (
	firstClient     = "198.51.100.1:40000"
	secondClient    = "198.51.100.2:40000"
	proxyPeer       = "10.0.0.1:40000"
	firstForwarded  = "203.0.113.1"
	secondForwarded = "203.0.113.2"
)

// csrfFieldPattern extracts the CSRF token rendered into the login form.
var csrfFieldPattern = regexp.MustCompile(
	`name="gorilla\.csrf\.Token" value="([^"]+)"`)

// newTestServer builds the server's real routes from the constructors
// cmd/pixad uses, with a throwaway state directory. Debug marks requests
// as plain HTTP, so the CSRF check runs without an https Referer.
func newTestServer(t *testing.T) *Server {
	t.Helper()

	stateDir := t.TempDir()
	cfg := &config.Config{
		Debug:             true,
		SigningKey:        testSigningKey,
		StateDir:          stateDir,
		DBURL:             "file:" + filepath.Join(stateDir, "state.sqlite3"),
		TrustedProxies:    []netip.Prefix{netip.MustParsePrefix("10.0.0.0/8")},
		DownstreamTimeout: config.DefaultDownstreamTimeout,
	}

	return startPixa(t, cfg)
}

// clientRequest builds a request for / arriving from remoteAddr, carrying
// forwardedFor as its X-Forwarded-For header when that is not empty.
func clientRequest(
	t *testing.T, method string, body io.Reader, remoteAddr, forwardedFor string,
) *http.Request {
	t.Helper()

	req := httptest.NewRequestWithContext(t.Context(), method, "/", body)
	req.RemoteAddr = remoteAddr

	if forwardedFor != "" {
		req.Header.Set("X-Forwarded-For", forwardedFor)
	}

	return req
}

// postLogin loads the login form with GET / and submits key in it with
// POST /, as a browser does, both from the same client. GET / is not rate
// limited, so the form must load even for a client over the limit.
func postLogin(
	t *testing.T, s *Server, remoteAddr, forwardedFor, key string,
) *httptest.ResponseRecorder {
	t.Helper()

	page := httptest.NewRecorder()
	s.ServeHTTP(page,
		clientRequest(t, http.MethodGet, nil, remoteAddr, forwardedFor))

	if page.Code != http.StatusOK {
		t.Fatalf("GET / status = %d, want %d", page.Code, http.StatusOK)
	}

	match := csrfFieldPattern.FindStringSubmatch(page.Body.String())
	if match == nil {
		t.Fatalf("no CSRF token field found in the login form")
	}

	form := url.Values{"key": {key}, "gorilla.csrf.Token": {match[1]}}
	req := clientRequest(t, http.MethodPost,
		strings.NewReader(form.Encode()), remoteAddr, forwardedFor)
	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")

	for _, c := range page.Result().Cookies() {
		req.AddCookie(c)
	}

	rec := httptest.NewRecorder()
	s.ServeHTTP(rec, req)

	return rec
}

// tripLoginRateLimit makes LoginAttemptsPerMinute failed logins from one
// client, each answered with the login form again, then one more, which
// must be refused with 429. It returns the response to that last attempt.
func tripLoginRateLimit(
	t *testing.T, s *Server, remoteAddr, forwardedFor string,
) *httptest.ResponseRecorder {
	t.Helper()

	for attempt := range LoginAttemptsPerMinute {
		rec := postLogin(t, s, remoteAddr, forwardedFor, wrongKey)
		if rec.Code != http.StatusOK {
			t.Fatalf("failed login %d status = %d, want %d",
				attempt+1, rec.Code, http.StatusOK)
		}
	}

	rec := postLogin(t, s, remoteAddr, forwardedFor, wrongKey)
	if rec.Code != http.StatusTooManyRequests {
		t.Fatalf("login over the limit status = %d, want %d",
			rec.Code, http.StatusTooManyRequests)
	}

	return rec
}

// TestLoginRateLimitRefusesAttemptOverLimit verifies the login attempt
// after LoginAttemptsPerMinute failed ones from one client is refused with
// 429 and a Retry-After header, and that the client cannot get around the
// limit by sending X-Forwarded-For: from a peer that is not a trusted
// proxy, the header is ignored.
func TestLoginRateLimitRefusesAttemptOverLimit(t *testing.T) {
	t.Parallel()

	s := newTestServer(t)

	rec := tripLoginRateLimit(t, s, firstClient, "")

	retryAfter := rec.Header().Get("Retry-After")

	seconds, err := strconv.Atoi(retryAfter)
	if err != nil || seconds <= 0 {
		t.Errorf("Retry-After = %q, want a positive number of seconds",
			retryAfter)
	}

	rec = postLogin(t, s, firstClient, secondForwarded, wrongKey)
	if rec.Code != http.StatusTooManyRequests {
		t.Errorf("login with X-Forwarded-For from an untrusted peer "+
			"status = %d, want %d", rec.Code, http.StatusTooManyRequests)
	}
}

// TestLoginRateLimitLeavesOtherClientsAlone verifies one client going over
// the limit does not limit another: a failed login from a different
// address is answered with the login form, and the signing key still logs
// it in.
func TestLoginRateLimitLeavesOtherClientsAlone(t *testing.T) {
	t.Parallel()

	s := newTestServer(t)

	tripLoginRateLimit(t, s, firstClient, "")

	rec := postLogin(t, s, secondClient, "", wrongKey)
	if rec.Code != http.StatusOK {
		t.Errorf("failed login from another client status = %d, want %d",
			rec.Code, http.StatusOK)
	}

	rec = postLogin(t, s, secondClient, "", testSigningKey)
	if rec.Code != http.StatusSeeOther {
		t.Errorf("login with the signing key from another client "+
			"status = %d, want %d", rec.Code, http.StatusSeeOther)
	}
}

// TestLoginRateLimitCountsClientsBehindProxySeparately verifies the limit
// counts the client address resolved from X-Forwarded-For, not the address
// of the trusted proxy the requests arrive from, so two clients behind the
// same proxy are counted separately.
func TestLoginRateLimitCountsClientsBehindProxySeparately(t *testing.T) {
	t.Parallel()

	s := newTestServer(t)

	tripLoginRateLimit(t, s, proxyPeer, firstForwarded)

	rec := postLogin(t, s, proxyPeer, secondForwarded, wrongKey)
	if rec.Code != http.StatusOK {
		t.Errorf("failed login from a second client behind the proxy "+
			"status = %d, want %d", rec.Code, http.StatusOK)
	}
}

// TestLoginRateLimitCountsIPv6ClientsByPrefix verifies an IPv6 client is
// counted by its /64: another address in the same /64 is refused too,
// while an address in a different /64 is not.
func TestLoginRateLimitCountsIPv6ClientsByPrefix(t *testing.T) {
	t.Parallel()

	s := newTestServer(t)

	tripLoginRateLimit(t, s, proxyPeer, "2001:db8::1")

	rec := postLogin(t, s, proxyPeer, "2001:db8::2", wrongKey)
	if rec.Code != http.StatusTooManyRequests {
		t.Errorf("login from the same /64 status = %d, want %d",
			rec.Code, http.StatusTooManyRequests)
	}

	rec = postLogin(t, s, proxyPeer, "2001:db8:0:1::1", wrongKey)
	if rec.Code != http.StatusOK {
		t.Errorf("login from another /64 status = %d, want %d",
			rec.Code, http.StatusOK)
	}
}

// TestLoginRateLimitCountsIPv4MappedClientsSeparately verifies an IPv4
// client that the proxy forwards in IPv4-mapped IPv6 form (::ffff:a.b.c.d)
// is counted by its IPv4 address, not by the /64 that every such address
// shares, so two of them behind the proxy are counted separately.
func TestLoginRateLimitCountsIPv4MappedClientsSeparately(t *testing.T) {
	t.Parallel()

	s := newTestServer(t)

	tripLoginRateLimit(t, s, proxyPeer, "::ffff:"+firstForwarded)

	rec := postLogin(t, s, proxyPeer, "::ffff:"+secondForwarded, wrongKey)
	if rec.Code != http.StatusOK {
		t.Errorf("failed login from a second IPv4-mapped client "+
			"status = %d, want %d", rec.Code, http.StatusOK)
	}
}