From 9be9ecb8106a5b20fc3b0228a23973a2c6189d14 Mon Sep 17 00:00:00 2001
From: bwees <brandonwees@gmail.com>
Date: Sat, 14 Nov 2026 13:33:00 -0600
Subject: [PATCH 1/3] feat: identify app sessions by X-App-Platform and
 X-App-Version headers

---
 apps/gateway/controllers/app_client.go   |  21 +++++
 apps/gateway/controllers/report.go       |   2 +-
 apps/gateway/controllers/version.go      |   2 +-
 apps/gateway/controllers/version_test.go | 106 +++++++++++++++++++----
 apps/gateway/cors_test.go                |  29 +++++--
 apps/gateway/dtos/app_client.go          |   8 ++
 apps/gateway/metrics/session.go          |   3 +-
 apps/gateway/services/report.go          |  21 +++--
 apps/gateway/services/session.go         |  35 ++++++--
 9 files changed, 185 insertions(+), 42 deletions(-)
 create mode 100644 apps/gateway/controllers/app_client.go
 create mode 100644 apps/gateway/dtos/app_client.go

diff --git a/apps/gateway/controllers/app_client.go b/apps/gateway/controllers/app_client.go
new file mode 100644
index 0000000..70ec782
--- /dev/null
+++ b/apps/gateway/controllers/app_client.go
@@ -0,0 +1,21 @@
+package controllers
+
+import (
+	"net/http"
+
+	"github.com/MaroonRides/api/apps/gateway/dtos"
+)
+
+// A browser cannot set its user agent, so the app names itself in these headers on every platform.
+const (
+	appPlatformHeader = "X-App-Platform"
+	appVersionHeader  = "X-App-Version"
+)
+
+func appClient(r *http.Request) dtos.AppClient {
+	return dtos.AppClient{
+		Platform:  r.Header.Get(appPlatformHeader),
+		Version:   r.Header.Get(appVersionHeader),
+		UserAgent: r.UserAgent(),
+	}
+}
diff --git a/apps/gateway/controllers/report.go b/apps/gateway/controllers/report.go
index d35e515..126cc1f 100644
--- a/apps/gateway/controllers/report.go
+++ b/apps/gateway/controllers/report.go
@@ -44,7 +44,7 @@ func (c *ReportController) report(fc fuego.ContextWithBody[dtos.ReportRequest])
 		return nil, err
 	}
 
-	err = c.svc.Record(req, fc.Request().UserAgent())
+	err = c.svc.Record(req, appClient(fc.Request()))
 	if errors.Is(err, services.ErrInvalidReport) {
 		return nil, fuego.BadRequestError{Detail: err.Error(), Err: err}
 	}
diff --git a/apps/gateway/controllers/version.go b/apps/gateway/controllers/version.go
index bb6395b..383d37e 100644
--- a/apps/gateway/controllers/version.go
+++ b/apps/gateway/controllers/version.go
@@ -28,7 +28,7 @@ type SupportedVersionResponse struct {
 
 // The app checks its version once per launch, so each call is one session.
 func (c *VersionController) supportedVersion(fc fuego.ContextNoBody) (SupportedVersionResponse, error) {
-	c.sessions.Started(fc.Request().UserAgent())
+	c.sessions.Started(appClient(fc.Request()))
 	return SupportedVersionResponse{
 		Version: config.MinimumSupportedVersion,
 	}, nil
diff --git a/apps/gateway/controllers/version_test.go b/apps/gateway/controllers/version_test.go
index f9a8108..a1421b5 100644
--- a/apps/gateway/controllers/version_test.go
+++ b/apps/gateway/controllers/version_test.go
@@ -17,7 +17,20 @@ import (
 	"github.com/MaroonRides/api/apps/gateway/services"
 )
 
-const appSessionsMetric = "gateway_app_sessions_total"
+const (
+	appSessionsMetric = "gateway_app_sessions_total"
+	appSessionsHeader = `
+# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
+# TYPE gateway_app_sessions_total counter
+`
+	browserUserAgent = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)"
+)
+
+type appRequest struct {
+	platform  string
+	version   string
+	userAgent string
+}
 
 var _ = Describe("VersionController", Label("unit"), func() {
 	var (
@@ -32,41 +45,96 @@ var _ = Describe("VersionController", Label("unit"), func() {
 		handler = server.Mux
 	})
 
-	checkVersion := func(userAgent string) {
+	checkVersion := func(app appRequest) {
 		req := httptest.NewRequest(http.MethodGet, "/api/version/supported", nil)
-		req.Header.Set("User-Agent", userAgent)
+		req.Header.Set("User-Agent", app.userAgent)
+		if app.platform != "" {
+			req.Header.Set("X-App-Platform", app.platform)
+		}
+		if app.version != "" {
+			req.Header.Set("X-App-Version", app.version)
+		}
 		res := httptest.NewRecorder()
 		handler.ServeHTTP(res, req)
 		ExpectWithOffset(1, res.Code).To(Equal(http.StatusOK))
 	}
 
-	It("counts a session by platform and app version", func() {
-		checkVersion("Maroon Rides App (iOS) v3.0.0")
-		checkVersion("Maroon Rides App (iOS) v3.0.0")
-		checkVersion("Maroon Rides App (Android) v3.0.1")
+	expectSessions := func(series string) {
+		ExpectWithOffset(1, testutil.GatherAndCompare(registry, strings.NewReader(appSessionsHeader+series), appSessionsMetric)).To(Succeed())
+	}
 
-		Expect(testutil.GatherAndCompare(registry, strings.NewReader(`
-# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
-# TYPE gateway_app_sessions_total counter
+	It("counts a session by the platform and version headers", func() {
+		checkVersion(appRequest{platform: "ios", version: "3.0.2"})
+		checkVersion(appRequest{platform: "ios", version: "3.0.2"})
+		checkVersion(appRequest{platform: "android", version: "3.0.2"})
+		checkVersion(appRequest{platform: "web", version: "3.0.2", userAgent: browserUserAgent})
+
+		expectSessions(`
+gateway_app_sessions_total{platform="android",version="3.0.2"} 1
+gateway_app_sessions_total{platform="ios",version="3.0.2"} 2
+gateway_app_sessions_total{platform="web",version="3.0.2"} 1
+`)
+	})
+
+	It("prefers the headers over the user agent", func() {
+		checkVersion(appRequest{platform: "android", version: "3.1.0", userAgent: "Maroon Rides App (iOS) v3.0.0"})
+
+		expectSessions(`
+gateway_app_sessions_total{platform="android",version="3.1.0"} 1
+`)
+	})
+
+	It("counts a build that only names itself in the user agent", func() {
+		checkVersion(appRequest{userAgent: "Maroon Rides App (iOS) v3.0.0"})
+		checkVersion(appRequest{userAgent: "Maroon Rides App (iOS) v3.0.0"})
+		checkVersion(appRequest{userAgent: "Maroon Rides App (Android) v3.0.1"})
+
+		expectSessions(`
 gateway_app_sessions_total{platform="android",version="3.0.1"} 1
 gateway_app_sessions_total{platform="ios",version="3.0.0"} 2
-`), appSessionsMetric)).To(Succeed())
+`)
 	})
 
-	It("leaves out callers that are not the app", func() {
-		checkVersion("kube-probe/1.34")
-		checkVersion("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)")
+	DescribeTable("falls back to the user agent when the headers are not usable",
+		func(platform, version string) {
+			checkVersion(appRequest{platform: platform, version: version, userAgent: "Maroon Rides App (Android) v3.0.1"})
 
-		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(BeZero())
-	})
+			expectSessions(`
+gateway_app_sessions_total{platform="android",version="3.0.1"} 1
+`)
+		},
+		Entry("platform only", "web", ""),
+		Entry("version only", "", "3.0.2"),
+		Entry("unknown platform", "electron", "3.0.2"),
+		Entry("platform not lowercase", "iOS", "3.0.2"),
+		Entry("version with a v prefix", "web", "v3.0.2"),
+		Entry("version missing a part", "web", "3.0"),
+		Entry("version with a prerelease", "web", "3.0.2-beta.1"),
+		Entry("version that is not a number", "web", "latest"),
+	)
+
+	DescribeTable("leaves out callers that are not the app",
+		func(app appRequest) {
+			checkVersion(app)
+
+			Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(BeZero())
+		},
+		Entry("kubelet probe", appRequest{userAgent: "kube-probe/1.34"}),
+		Entry("browser", appRequest{userAgent: browserUserAgent}),
+		Entry("browser with a bad platform header", appRequest{platform: "linux", version: "3.0.2", userAgent: browserUserAgent}),
+		Entry("browser with a bad version header", appRequest{platform: "web", version: "3", userAgent: browserUserAgent}),
+	)
 
 	It("folds versions past the cap into one label", func() {
 		for patch := range 60 {
-			checkVersion(fmt.Sprintf("Maroon Rides App (iOS) v3.0.%d", patch))
+			checkVersion(appRequest{platform: "web", version: fmt.Sprintf("3.0.%d", patch)})
 		}
 
 		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(51))
-		checkVersion("Maroon Rides App (iOS) v3.0.0")
-		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(51))
+		checkVersion(appRequest{userAgent: "Maroon Rides App (iOS) v3.0.0"})
+		checkVersion(appRequest{platform: "web", version: "3.0.0"})
+		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(52))
+		checkVersion(appRequest{platform: "web", version: "4.0.0"})
+		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(52))
 	})
 })
diff --git a/apps/gateway/cors_test.go b/apps/gateway/cors_test.go
index fcaa83f..a0e8fb5 100644
--- a/apps/gateway/cors_test.go
+++ b/apps/gateway/cors_test.go
@@ -9,21 +9,34 @@ import (
 )
 
 var _ = Describe("CORS", Label("unit"), func() {
+	preflight := func(origin, method, headers string) *httptest.ResponseRecorder {
+		handler := corsMiddleware(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
+		req := httptest.NewRequest(http.MethodOptions, "/api/sync/stream", nil)
+		req.Header.Set("Origin", origin)
+		req.Header.Set("Access-Control-Request-Method", method)
+		req.Header.Set("Access-Control-Request-Headers", headers)
+
+		res := httptest.NewRecorder()
+		handler.ServeHTTP(res, req)
+		return res
+	}
+
 	DescribeTable("allows any origin",
 		func(origin string) {
-			handler := corsMiddleware(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
-			req := httptest.NewRequest(http.MethodOptions, "/api/sync/stream", nil)
-			req.Header.Set("Origin", origin)
-			req.Header.Set("Access-Control-Request-Method", http.MethodPost)
-			req.Header.Set("Access-Control-Request-Headers", "content-type")
-
-			res := httptest.NewRecorder()
-			handler.ServeHTTP(res, req)
+			res := preflight(origin, http.MethodPost, "content-type")
 
 			Expect(res.Header().Get("Access-Control-Allow-Origin")).To(Equal("*"))
 		},
 		Entry("iOS app", "capacitor://localhost"),
 		Entry("Android app", "https://localhost"),
+		Entry("web app", "https://web.maroonrides.app"),
 		Entry("Vite dev server", "http://100.89.139.58:5173"),
 	)
+
+	It("allows the headers the app names itself with", func() {
+		res := preflight("https://web.maroonrides.app", http.MethodGet, "x-app-platform,x-app-version")
+
+		Expect(res.Header().Get("Access-Control-Allow-Origin")).To(Equal("*"))
+		Expect(res.Header().Get("Access-Control-Allow-Headers")).To(Equal("x-app-platform,x-app-version"))
+	})
 })
diff --git a/apps/gateway/dtos/app_client.go b/apps/gateway/dtos/app_client.go
new file mode 100644
index 0000000..90f4082
--- /dev/null
+++ b/apps/gateway/dtos/app_client.go
@@ -0,0 +1,8 @@
+package dtos
+
+// AppClient is what a request says about the app that sent it. Every field comes from the caller and is untrusted.
+type AppClient struct {
+	Platform  string
+	Version   string
+	UserAgent string
+}
diff --git a/apps/gateway/metrics/session.go b/apps/gateway/metrics/session.go
index 0d5801e..7166a4a 100644
--- a/apps/gateway/metrics/session.go
+++ b/apps/gateway/metrics/session.go
@@ -10,7 +10,7 @@ const (
 	labelPlatform = "platform"
 	labelVersion  = "version"
 
-	// Versions past this many share one label so a forged user agent cannot grow the series count.
+	// Versions past this many share one label so a forged client cannot grow the series count.
 	maxAppVersions  = 50
 	OtherAppVersion = "other"
 )
@@ -20,6 +20,7 @@ type AppPlatform string
 const (
 	AppPlatformIOS     AppPlatform = "ios"
 	AppPlatformAndroid AppPlatform = "android"
+	AppPlatformWeb     AppPlatform = "web"
 )
 
 type SessionMetrics struct {
diff --git a/apps/gateway/services/report.go b/apps/gateway/services/report.go
index cb451e4..6185ef3 100644
--- a/apps/gateway/services/report.go
+++ b/apps/gateway/services/report.go
@@ -68,27 +68,28 @@ func NewReportService(syncMetrics *metrics.SyncMetrics, reportMetrics *metrics.R
 }
 
 // Record drops a bad event instead of failing the request, so one event a gateway cannot read never loses the rest.
-func (s *ReportService) Record(req dtos.ReportRequest, userAgent string) error {
+func (s *ReportService) Record(req dtos.ReportRequest, client dtos.AppClient) error {
 	if len(req.Events) > maxReportEvents {
 		return fmt.Errorf("%w: %d events is more than %d", ErrInvalidReport, len(req.Events), maxReportEvents)
 	}
+	clientAttr := clientLog(client)
 	for _, event := range req.Events {
-		s.record(event, truncate(userAgent, maxReportedMessage))
+		s.record(event, clientAttr)
 	}
 	return nil
 }
 
-func (s *ReportService) record(event dtos.ReportEvent, userAgent string) {
+func (s *ReportService) record(event dtos.ReportEvent, client slog.Attr) {
 	decode, ok := syncFailureDecoders[event.Type]
 	if !ok {
-		slog.Warn("dropped report event with unknown type", "type", truncate(string(event.Type), maxReportedMessage), "userAgent", userAgent)
+		slog.Warn("dropped report event with unknown type", "type", truncate(string(event.Type), maxReportedMessage), client)
 		s.reportMetrics.Received(metrics.UnknownReportType, metrics.ReportDropped)
 		return
 	}
 
 	failure, err := decode(event.Payload)
 	if err != nil {
-		slog.Warn("dropped report event with bad payload", "type", event.Type, "error", err, "userAgent", userAgent)
+		slog.Warn("dropped report event with bad payload", "type", event.Type, "error", err, client)
 		s.reportMetrics.Received(string(event.Type), metrics.ReportDropped)
 		return
 	}
@@ -107,7 +108,7 @@ func (s *ReportService) record(event dtos.ReportEvent, userAgent string) {
 		"status", failure.status,
 		"message", truncate(failure.message, maxReportedMessage),
 		"acks", failure.acks,
-		"userAgent", userAgent,
+		client,
 	)
 }
 
@@ -117,3 +118,11 @@ func truncate(s string, limit int) string {
 	}
 	return s[:limit]
 }
+
+func clientLog(client dtos.AppClient) slog.Attr {
+	return slog.Group("client",
+		"platform", truncate(client.Platform, maxReportedMessage),
+		"version", truncate(client.Version, maxReportedMessage),
+		"userAgent", truncate(client.UserAgent, maxReportedMessage),
+	)
+}
diff --git a/apps/gateway/services/session.go b/apps/gateway/services/session.go
index 57b4afb..c179c51 100644
--- a/apps/gateway/services/session.go
+++ b/apps/gateway/services/session.go
@@ -3,13 +3,23 @@ package services
 import (
 	"regexp"
 
+	"github.com/MaroonRides/api/apps/gateway/dtos"
 	"github.com/MaroonRides/api/apps/gateway/metrics"
 )
 
-// The app sets its user agent in capacitor.config.ts, e.g. "Maroon Rides App (iOS) v3.0.0".
+var appVersion = regexp.MustCompile(`^\d+\.\d+\.\d+$`)
+
+// Values of the X-App-Platform header, as Capacitor's getPlatform() returns them.
+var headerPlatforms = map[string]metrics.AppPlatform{
+	"ios":     metrics.AppPlatformIOS,
+	"android": metrics.AppPlatformAndroid,
+	"web":     metrics.AppPlatformWeb,
+}
+
+// Builds from before the app sent its own headers only name themselves here, set in capacitor.config.ts, e.g. "Maroon Rides App (iOS) v3.0.0".
 var appUserAgent = regexp.MustCompile(`Maroon Rides App \((iOS|Android)\) v(\d+\.\d+\.\d+)`)
 
-var appPlatforms = map[string]metrics.AppPlatform{
+var userAgentPlatforms = map[string]metrics.AppPlatform{
 	"iOS":     metrics.AppPlatformIOS,
 	"Android": metrics.AppPlatformAndroid,
 }
@@ -23,10 +33,23 @@ func NewSessionService(m *metrics.SessionMetrics) *SessionService {
 }
 
 // Started ignores anything that is not the app, since the kubelet probes the same endpoint.
-func (s *SessionService) Started(userAgent string) {
-	match := appUserAgent.FindStringSubmatch(userAgent)
-	if match == nil {
+func (s *SessionService) Started(client dtos.AppClient) {
+	platform, version, ok := identifyApp(client)
+	if !ok {
 		return
 	}
-	s.metrics.Started(appPlatforms[match[1]], match[2])
+	s.metrics.Started(platform, version)
+}
+
+func identifyApp(client dtos.AppClient) (metrics.AppPlatform, string, bool) {
+	platform, known := headerPlatforms[client.Platform]
+	if known && appVersion.MatchString(client.Version) {
+		return platform, client.Version, true
+	}
+
+	match := appUserAgent.FindStringSubmatch(client.UserAgent)
+	if match == nil {
+		return "", "", false
+	}
+	return userAgentPlatforms[match[1]], match[2], true
 }

From d8d7de72030b121e4baf718aec6fd178ff3a0136 Mon Sep 17 00:00:00 2001
From: bwees <brandonwees@gmail.com>
Date: Sat, 14 Nov 2026 13:41:27 -0600
Subject: [PATCH 2/3] refactor: move app client header parsing to gateway utils

---
 apps/gateway/controllers/report.go                | 3 ++-
 apps/gateway/controllers/version.go               | 3 ++-
 apps/gateway/{controllers => utils}/app_client.go | 4 ++--
 3 files changed, 6 insertions(+), 4 deletions(-)
 rename apps/gateway/{controllers => utils}/app_client.go (85%)

diff --git a/apps/gateway/controllers/report.go b/apps/gateway/controllers/report.go
index 126cc1f..9cf99b8 100644
--- a/apps/gateway/controllers/report.go
+++ b/apps/gateway/controllers/report.go
@@ -8,6 +8,7 @@ import (
 
 	"github.com/MaroonRides/api/apps/gateway/dtos"
 	"github.com/MaroonRides/api/apps/gateway/services"
+	"github.com/MaroonRides/api/apps/gateway/utils"
 )
 
 const maxReportBodyBytes = 256 << 10
@@ -44,7 +45,7 @@ func (c *ReportController) report(fc fuego.ContextWithBody[dtos.ReportRequest])
 		return nil, err
 	}
 
-	err = c.svc.Record(req, appClient(fc.Request()))
+	err = c.svc.Record(req, utils.AppClient(fc.Request()))
 	if errors.Is(err, services.ErrInvalidReport) {
 		return nil, fuego.BadRequestError{Detail: err.Error(), Err: err}
 	}
diff --git a/apps/gateway/controllers/version.go b/apps/gateway/controllers/version.go
index 383d37e..804649b 100644
--- a/apps/gateway/controllers/version.go
+++ b/apps/gateway/controllers/version.go
@@ -5,6 +5,7 @@ import (
 
 	"github.com/MaroonRides/api/apps/gateway/config"
 	"github.com/MaroonRides/api/apps/gateway/services"
+	"github.com/MaroonRides/api/apps/gateway/utils"
 )
 
 type VersionController struct {
@@ -28,7 +29,7 @@ type SupportedVersionResponse struct {
 
 // The app checks its version once per launch, so each call is one session.
 func (c *VersionController) supportedVersion(fc fuego.ContextNoBody) (SupportedVersionResponse, error) {
-	c.sessions.Started(appClient(fc.Request()))
+	c.sessions.Started(utils.AppClient(fc.Request()))
 	return SupportedVersionResponse{
 		Version: config.MinimumSupportedVersion,
 	}, nil
diff --git a/apps/gateway/controllers/app_client.go b/apps/gateway/utils/app_client.go
similarity index 85%
rename from apps/gateway/controllers/app_client.go
rename to apps/gateway/utils/app_client.go
index 70ec782..f1878d0 100644
--- a/apps/gateway/controllers/app_client.go
+++ b/apps/gateway/utils/app_client.go
@@ -1,4 +1,4 @@
-package controllers
+package utils
 
 import (
 	"net/http"
@@ -12,7 +12,7 @@ const (
 	appVersionHeader  = "X-App-Version"
 )
 
-func appClient(r *http.Request) dtos.AppClient {
+func AppClient(r *http.Request) dtos.AppClient {
 	return dtos.AppClient{
 		Platform:  r.Header.Get(appPlatformHeader),
 		Version:   r.Header.Get(appVersionHeader),

From ee77b70ba863620258c8568cac5c93f2b3f73438 Mon Sep 17 00:00:00 2001
From: bwees <brandonwees@gmail.com>
Date: Sat, 14 Nov 2026 13:42:49 -0600
Subject: [PATCH 3/3] refactor: slim app session header handling

---
 apps/gateway/controllers/report.go       |   3 +-
 apps/gateway/controllers/version.go      |   3 +-
 apps/gateway/controllers/version_test.go | 121 ++++++++---------------
 apps/gateway/cors_test.go                |  29 ++----
 apps/gateway/dtos/app_client.go          |   8 --
 apps/gateway/services/report.go          |  21 ++--
 apps/gateway/services/session.go         |  21 ++--
 apps/gateway/utils/app_client.go         |  18 +---
 8 files changed, 69 insertions(+), 155 deletions(-)
 delete mode 100644 apps/gateway/dtos/app_client.go

diff --git a/apps/gateway/controllers/report.go b/apps/gateway/controllers/report.go
index 9cf99b8..d35e515 100644
--- a/apps/gateway/controllers/report.go
+++ b/apps/gateway/controllers/report.go
@@ -8,7 +8,6 @@ import (
 
 	"github.com/MaroonRides/api/apps/gateway/dtos"
 	"github.com/MaroonRides/api/apps/gateway/services"
-	"github.com/MaroonRides/api/apps/gateway/utils"
 )
 
 const maxReportBodyBytes = 256 << 10
@@ -45,7 +44,7 @@ func (c *ReportController) report(fc fuego.ContextWithBody[dtos.ReportRequest])
 		return nil, err
 	}
 
-	err = c.svc.Record(req, utils.AppClient(fc.Request()))
+	err = c.svc.Record(req, fc.Request().UserAgent())
 	if errors.Is(err, services.ErrInvalidReport) {
 		return nil, fuego.BadRequestError{Detail: err.Error(), Err: err}
 	}
diff --git a/apps/gateway/controllers/version.go b/apps/gateway/controllers/version.go
index 804649b..d6b7b91 100644
--- a/apps/gateway/controllers/version.go
+++ b/apps/gateway/controllers/version.go
@@ -29,7 +29,8 @@ type SupportedVersionResponse struct {
 
 // The app checks its version once per launch, so each call is one session.
 func (c *VersionController) supportedVersion(fc fuego.ContextNoBody) (SupportedVersionResponse, error) {
-	c.sessions.Started(utils.AppClient(fc.Request()))
+	r := fc.Request()
+	c.sessions.Started(r.Header.Get(utils.AppPlatformHeader), r.Header.Get(utils.AppVersionHeader), r.UserAgent())
 	return SupportedVersionResponse{
 		Version: config.MinimumSupportedVersion,
 	}, nil
diff --git a/apps/gateway/controllers/version_test.go b/apps/gateway/controllers/version_test.go
index a1421b5..fce10d4 100644
--- a/apps/gateway/controllers/version_test.go
+++ b/apps/gateway/controllers/version_test.go
@@ -17,20 +17,7 @@ import (
 	"github.com/MaroonRides/api/apps/gateway/services"
 )
 
-const (
-	appSessionsMetric = "gateway_app_sessions_total"
-	appSessionsHeader = `
-# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
-# TYPE gateway_app_sessions_total counter
-`
-	browserUserAgent = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)"
-)
-
-type appRequest struct {
-	platform  string
-	version   string
-	userAgent string
-}
+const appSessionsMetric = "gateway_app_sessions_total"
 
 var _ = Describe("VersionController", Label("unit"), func() {
 	var (
@@ -45,96 +32,74 @@ var _ = Describe("VersionController", Label("unit"), func() {
 		handler = server.Mux
 	})
 
-	checkVersion := func(app appRequest) {
+	checkVersionWithHeaders := func(platform, version, userAgent string) {
 		req := httptest.NewRequest(http.MethodGet, "/api/version/supported", nil)
-		req.Header.Set("User-Agent", app.userAgent)
-		if app.platform != "" {
-			req.Header.Set("X-App-Platform", app.platform)
-		}
-		if app.version != "" {
-			req.Header.Set("X-App-Version", app.version)
-		}
+		req.Header.Set("X-App-Platform", platform)
+		req.Header.Set("X-App-Version", version)
+		req.Header.Set("User-Agent", userAgent)
 		res := httptest.NewRecorder()
 		handler.ServeHTTP(res, req)
 		ExpectWithOffset(1, res.Code).To(Equal(http.StatusOK))
 	}
 
-	expectSessions := func(series string) {
-		ExpectWithOffset(1, testutil.GatherAndCompare(registry, strings.NewReader(appSessionsHeader+series), appSessionsMetric)).To(Succeed())
+	checkVersion := func(userAgent string) {
+		checkVersionWithHeaders("", "", userAgent)
 	}
 
-	It("counts a session by the platform and version headers", func() {
-		checkVersion(appRequest{platform: "ios", version: "3.0.2"})
-		checkVersion(appRequest{platform: "ios", version: "3.0.2"})
-		checkVersion(appRequest{platform: "android", version: "3.0.2"})
-		checkVersion(appRequest{platform: "web", version: "3.0.2", userAgent: browserUserAgent})
-
-		expectSessions(`
-gateway_app_sessions_total{platform="android",version="3.0.2"} 1
-gateway_app_sessions_total{platform="ios",version="3.0.2"} 2
-gateway_app_sessions_total{platform="web",version="3.0.2"} 1
-`)
-	})
-
-	It("prefers the headers over the user agent", func() {
-		checkVersion(appRequest{platform: "android", version: "3.1.0", userAgent: "Maroon Rides App (iOS) v3.0.0"})
+	It("counts a session from the platform and version headers, ahead of the user agent", func() {
+		checkVersionWithHeaders("web", "3.0.2", "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)")
+		checkVersionWithHeaders("android", "3.1.0", "Maroon Rides App (iOS) v3.0.0")
 
-		expectSessions(`
+		Expect(testutil.GatherAndCompare(registry, strings.NewReader(`
+# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
+# TYPE gateway_app_sessions_total counter
 gateway_app_sessions_total{platform="android",version="3.1.0"} 1
-`)
-	})
-
-	It("counts a build that only names itself in the user agent", func() {
-		checkVersion(appRequest{userAgent: "Maroon Rides App (iOS) v3.0.0"})
-		checkVersion(appRequest{userAgent: "Maroon Rides App (iOS) v3.0.0"})
-		checkVersion(appRequest{userAgent: "Maroon Rides App (Android) v3.0.1"})
-
-		expectSessions(`
-gateway_app_sessions_total{platform="android",version="3.0.1"} 1
-gateway_app_sessions_total{platform="ios",version="3.0.0"} 2
-`)
+gateway_app_sessions_total{platform="web",version="3.0.2"} 1
+`), appSessionsMetric)).To(Succeed())
 	})
 
-	DescribeTable("falls back to the user agent when the headers are not usable",
+	DescribeTable("falls back to the user agent when a header is missing or malformed",
 		func(platform, version string) {
-			checkVersion(appRequest{platform: platform, version: version, userAgent: "Maroon Rides App (Android) v3.0.1"})
+			checkVersionWithHeaders(platform, version, "Maroon Rides App (Android) v3.0.1")
 
-			expectSessions(`
+			Expect(testutil.GatherAndCompare(registry, strings.NewReader(`
+# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
+# TYPE gateway_app_sessions_total counter
 gateway_app_sessions_total{platform="android",version="3.0.1"} 1
-`)
+`), appSessionsMetric)).To(Succeed())
 		},
-		Entry("platform only", "web", ""),
-		Entry("version only", "", "3.0.2"),
+		Entry("no version", "web", ""),
 		Entry("unknown platform", "electron", "3.0.2"),
-		Entry("platform not lowercase", "iOS", "3.0.2"),
 		Entry("version with a v prefix", "web", "v3.0.2"),
-		Entry("version missing a part", "web", "3.0"),
-		Entry("version with a prerelease", "web", "3.0.2-beta.1"),
-		Entry("version that is not a number", "web", "latest"),
 	)
 
-	DescribeTable("leaves out callers that are not the app",
-		func(app appRequest) {
-			checkVersion(app)
+	It("counts a session by platform and app version", func() {
+		checkVersion("Maroon Rides App (iOS) v3.0.0")
+		checkVersion("Maroon Rides App (iOS) v3.0.0")
+		checkVersion("Maroon Rides App (Android) v3.0.1")
 
-			Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(BeZero())
-		},
-		Entry("kubelet probe", appRequest{userAgent: "kube-probe/1.34"}),
-		Entry("browser", appRequest{userAgent: browserUserAgent}),
-		Entry("browser with a bad platform header", appRequest{platform: "linux", version: "3.0.2", userAgent: browserUserAgent}),
-		Entry("browser with a bad version header", appRequest{platform: "web", version: "3", userAgent: browserUserAgent}),
-	)
+		Expect(testutil.GatherAndCompare(registry, strings.NewReader(`
+# HELP gateway_app_sessions_total App launches, counted by the version check each launch makes, by platform and app version.
+# TYPE gateway_app_sessions_total counter
+gateway_app_sessions_total{platform="android",version="3.0.1"} 1
+gateway_app_sessions_total{platform="ios",version="3.0.0"} 2
+`), appSessionsMetric)).To(Succeed())
+	})
+
+	It("leaves out callers that are not the app", func() {
+		checkVersion("kube-probe/1.34")
+		checkVersion("Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)")
+
+		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(BeZero())
+	})
 
 	It("folds versions past the cap into one label", func() {
 		for patch := range 60 {
-			checkVersion(appRequest{platform: "web", version: fmt.Sprintf("3.0.%d", patch)})
+			checkVersion(fmt.Sprintf("Maroon Rides App (iOS) v3.0.%d", patch))
 		}
 
 		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(51))
-		checkVersion(appRequest{userAgent: "Maroon Rides App (iOS) v3.0.0"})
-		checkVersion(appRequest{platform: "web", version: "3.0.0"})
-		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(52))
-		checkVersion(appRequest{platform: "web", version: "4.0.0"})
-		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(52))
+		checkVersion("Maroon Rides App (iOS) v3.0.0")
+		Expect(testutil.CollectAndCount(registry, appSessionsMetric)).To(Equal(51))
 	})
 })
diff --git a/apps/gateway/cors_test.go b/apps/gateway/cors_test.go
index a0e8fb5..c980b79 100644
--- a/apps/gateway/cors_test.go
+++ b/apps/gateway/cors_test.go
@@ -9,34 +9,23 @@ import (
 )
 
 var _ = Describe("CORS", Label("unit"), func() {
-	preflight := func(origin, method, headers string) *httptest.ResponseRecorder {
-		handler := corsMiddleware(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
-		req := httptest.NewRequest(http.MethodOptions, "/api/sync/stream", nil)
-		req.Header.Set("Origin", origin)
-		req.Header.Set("Access-Control-Request-Method", method)
-		req.Header.Set("Access-Control-Request-Headers", headers)
-
-		res := httptest.NewRecorder()
-		handler.ServeHTTP(res, req)
-		return res
-	}
-
 	DescribeTable("allows any origin",
 		func(origin string) {
-			res := preflight(origin, http.MethodPost, "content-type")
+			handler := corsMiddleware(http.HandlerFunc(func(http.ResponseWriter, *http.Request) {}))
+			req := httptest.NewRequest(http.MethodOptions, "/api/sync/stream", nil)
+			req.Header.Set("Origin", origin)
+			req.Header.Set("Access-Control-Request-Method", http.MethodPost)
+			req.Header.Set("Access-Control-Request-Headers", "content-type,x-app-platform,x-app-version")
+
+			res := httptest.NewRecorder()
+			handler.ServeHTTP(res, req)
 
 			Expect(res.Header().Get("Access-Control-Allow-Origin")).To(Equal("*"))
+			Expect(res.Header().Get("Access-Control-Allow-Headers")).To(Equal("content-type,x-app-platform,x-app-version"))
 		},
 		Entry("iOS app", "capacitor://localhost"),
 		Entry("Android app", "https://localhost"),
 		Entry("web app", "https://web.maroonrides.app"),
 		Entry("Vite dev server", "http://100.89.139.58:5173"),
 	)
-
-	It("allows the headers the app names itself with", func() {
-		res := preflight("https://web.maroonrides.app", http.MethodGet, "x-app-platform,x-app-version")
-
-		Expect(res.Header().Get("Access-Control-Allow-Origin")).To(Equal("*"))
-		Expect(res.Header().Get("Access-Control-Allow-Headers")).To(Equal("x-app-platform,x-app-version"))
-	})
 })
diff --git a/apps/gateway/dtos/app_client.go b/apps/gateway/dtos/app_client.go
deleted file mode 100644
index 90f4082..0000000
--- a/apps/gateway/dtos/app_client.go
+++ /dev/null
@@ -1,8 +0,0 @@
-package dtos
-
-// AppClient is what a request says about the app that sent it. Every field comes from the caller and is untrusted.
-type AppClient struct {
-	Platform  string
-	Version   string
-	UserAgent string
-}
diff --git a/apps/gateway/services/report.go b/apps/gateway/services/report.go
index 6185ef3..cb451e4 100644
--- a/apps/gateway/services/report.go
+++ b/apps/gateway/services/report.go
@@ -68,28 +68,27 @@ func NewReportService(syncMetrics *metrics.SyncMetrics, reportMetrics *metrics.R
 }
 
 // Record drops a bad event instead of failing the request, so one event a gateway cannot read never loses the rest.
-func (s *ReportService) Record(req dtos.ReportRequest, client dtos.AppClient) error {
+func (s *ReportService) Record(req dtos.ReportRequest, userAgent string) error {
 	if len(req.Events) > maxReportEvents {
 		return fmt.Errorf("%w: %d events is more than %d", ErrInvalidReport, len(req.Events), maxReportEvents)
 	}
-	clientAttr := clientLog(client)
 	for _, event := range req.Events {
-		s.record(event, clientAttr)
+		s.record(event, truncate(userAgent, maxReportedMessage))
 	}
 	return nil
 }
 
-func (s *ReportService) record(event dtos.ReportEvent, client slog.Attr) {
+func (s *ReportService) record(event dtos.ReportEvent, userAgent string) {
 	decode, ok := syncFailureDecoders[event.Type]
 	if !ok {
-		slog.Warn("dropped report event with unknown type", "type", truncate(string(event.Type), maxReportedMessage), client)
+		slog.Warn("dropped report event with unknown type", "type", truncate(string(event.Type), maxReportedMessage), "userAgent", userAgent)
 		s.reportMetrics.Received(metrics.UnknownReportType, metrics.ReportDropped)
 		return
 	}
 
 	failure, err := decode(event.Payload)
 	if err != nil {
-		slog.Warn("dropped report event with bad payload", "type", event.Type, "error", err, client)
+		slog.Warn("dropped report event with bad payload", "type", event.Type, "error", err, "userAgent", userAgent)
 		s.reportMetrics.Received(string(event.Type), metrics.ReportDropped)
 		return
 	}
@@ -108,7 +107,7 @@ func (s *ReportService) record(event dtos.ReportEvent, client slog.Attr) {
 		"status", failure.status,
 		"message", truncate(failure.message, maxReportedMessage),
 		"acks", failure.acks,
-		client,
+		"userAgent", userAgent,
 	)
 }
 
@@ -118,11 +117,3 @@ func truncate(s string, limit int) string {
 	}
 	return s[:limit]
 }
-
-func clientLog(client dtos.AppClient) slog.Attr {
-	return slog.Group("client",
-		"platform", truncate(client.Platform, maxReportedMessage),
-		"version", truncate(client.Version, maxReportedMessage),
-		"userAgent", truncate(client.UserAgent, maxReportedMessage),
-	)
-}
diff --git a/apps/gateway/services/session.go b/apps/gateway/services/session.go
index c179c51..57cb8f2 100644
--- a/apps/gateway/services/session.go
+++ b/apps/gateway/services/session.go
@@ -3,7 +3,6 @@ package services
 import (
 	"regexp"
 
-	"github.com/MaroonRides/api/apps/gateway/dtos"
 	"github.com/MaroonRides/api/apps/gateway/metrics"
 )
 
@@ -33,23 +32,15 @@ func NewSessionService(m *metrics.SessionMetrics) *SessionService {
 }
 
 // Started ignores anything that is not the app, since the kubelet probes the same endpoint.
-func (s *SessionService) Started(client dtos.AppClient) {
-	platform, version, ok := identifyApp(client)
-	if !ok {
+func (s *SessionService) Started(platform, version, userAgent string) {
+	if p, ok := headerPlatforms[platform]; ok && appVersion.MatchString(version) {
+		s.metrics.Started(p, version)
 		return
 	}
-	s.metrics.Started(platform, version)
-}
-
-func identifyApp(client dtos.AppClient) (metrics.AppPlatform, string, bool) {
-	platform, known := headerPlatforms[client.Platform]
-	if known && appVersion.MatchString(client.Version) {
-		return platform, client.Version, true
-	}
 
-	match := appUserAgent.FindStringSubmatch(client.UserAgent)
+	match := appUserAgent.FindStringSubmatch(userAgent)
 	if match == nil {
-		return "", "", false
+		return
 	}
-	return userAgentPlatforms[match[1]], match[2], true
+	s.metrics.Started(userAgentPlatforms[match[1]], match[2])
 }
diff --git a/apps/gateway/utils/app_client.go b/apps/gateway/utils/app_client.go
index f1878d0..72f8c16 100644
--- a/apps/gateway/utils/app_client.go
+++ b/apps/gateway/utils/app_client.go
@@ -1,21 +1,7 @@
 package utils
 
-import (
-	"net/http"
-
-	"github.com/MaroonRides/api/apps/gateway/dtos"
-)
-
 // A browser cannot set its user agent, so the app names itself in these headers on every platform.
 const (
-	appPlatformHeader = "X-App-Platform"
-	appVersionHeader  = "X-App-Version"
+	AppPlatformHeader = "X-App-Platform"
+	AppVersionHeader  = "X-App-Version"
 )
-
-func AppClient(r *http.Request) dtos.AppClient {
-	return dtos.AppClient{
-		Platform:  r.Header.Get(appPlatformHeader),
-		Version:   r.Header.Get(appVersionHeader),
-		UserAgent: r.UserAgent(),
-	}
-}