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feat(expo): add native-to-web session transfer APIs - #10767
A signed-in Expo app can now open a web page that is already signed in as the same user. The page can open in a WebView the app renders or in the system browser. The SDK asks Clerk for a one-time sign-in URL, which is valid for 60 seconds, right before it opens the page. FAPI's session_transfers endpoints are live behind a per-instance flag.
@clerk/expo/native-to-web has three exports.
useAuthenticatedWebView({ destination }) prepares the URL when the screen mounts. It returns webViewProps to spread onto a react-native-webview<WebView>, and a status of preparing, ready, signed-out, or error. status stays preparing while the WebView is on Clerk's "Signing you in" page, so the app can keep its own overlay up until the destination loads. The hook matches the redeem page by origin and path, so it also works for instances behind a proxy. If redeem fails, the hook reads __clerk_error_code from the landing URL and reports it as error.code. It accepts both the current __clerk_status=failed and session_transfer_failed, which clerk_go #23983 changes it to.
useNativeToWeb().openExternalBrowser({ destination }) opens the default browser. iOS uses Linking.openURL. Android Chrome refuses an app-opened URL unless the intent names the app as referrer. On Android the opener starts a VIEW intent through expo-intent-launcher, with the String extra android.intent.extra.REFERRER_NAME set to android-app://<package>. Chrome ignores a String EXTRA_REFERRER, but it turns REFERRER_NAME into Referer: android-app://<package>/. That means @clerk/expo needs no native code of its own.
isSessionTransferError(error). Every failure is an Error & { code }. FAPI refusal codes and redeem codes pass through unchanged, and the ClerkAPIResponseError stays on cause.
@clerk/expo/native-to-web/advanced exports prepareSessionTransfer({ destination, presentation }) for apps that present the URL themselves. The url property of the returned object is not enumerable, so console.log and JSON.stringify leave it out.
React Strict Mode and remounts don't create a second live transfer. A module-level ledger hands an in-flight or unused transfer to the next presenter that asks for the same session and destination. A transfer is marked used as soon as its URL reaches a WebView or the browser.
The first commit moves the FAPI request helpers from utils/hostedAuth.ts to utils/fapiRequest.ts, and getExpoAppIdentifier from useHostedAuth.ts to utils/appIdentifier.ts. Hosted auth now uses the shared copies. Its behavior doesn't change and its tests are unchanged.
expo-intent-launcher is a new optional peer. react-native-webview is a devDependency for a type test only. Its props are typed structurally, so it is not a peer.
I ran it with an Expo SDK 58 app against a development instance that has the flag on, on an iPhone 18 Pro simulator (iOS 27) and an Android API 36 emulator with Chrome. Each path below ended signed in:
Path
iOS
Android
useAuthenticatedWebView
Signed in, ready
Signed in, ready
openExternalBrowser
Safari, signed in
Chrome via REFERRER_NAME, signed in
WebView mounted 65 s after mint
error: expired, retry() signs in
error: expired, retry() signs in
There is one known gap. On iOS, onLoadEnd for the destination fires before WebKit paints the new page. When the overlay drops, the "Signing you in" page shows for one frame, about 33 ms, then the destination paints. Android didn't show this.
Checklist
pnpm test runs as expected.
pnpm build runs as expected.
(If applicable) JSDoc comments have been added or updated for any package exports
The change adds Expo APIs to transfer a signed-in session to a native WebView or external browser. It adds transfer validation, error handling, transfer reuse, and WebView navigation status handling. Android browser launches use a VIEW intent with an app referrer. Shared FAPI response helpers are also used by hosted auth. Package exports, dependencies, documentation, and declaration typechecking are updated.
This adds opt-in native-to-web session transfer APIs and moves shared request helpers behind unchanged hosted-auth behavior. No concrete merge-blocking risk was identified in the supplied evidence. Normal checks on the built package entry points are still advisable.
Pre-merge checks: 4 · 1
Failed checks: 1 warning
Check name
Status
Explanation
Resolution
Docstring Coverage
Docstring coverage is 8.11% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…
Write docstrings for the functions missing them to satisfy the coverage threshold.
Passed checks: 4 passed
Check name
Status
Explanation
Title check
The title clearly and concisely identifies the main change: new native-to-web session transfer APIs for Expo.
Description check
The description directly explains the new Expo session transfer APIs, supported WebView and browser flows, dependencies, testing, and known limitations.
Linked Issues check
Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check
Check skipped because no linked issues were found for this pull request.
Full details: Docstring Coverage
Explanation
Docstring coverage is 8.11% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 37 functions across 22 files. (5 skipped: 5 unsupported.)
Resolution
Write docstrings for the functions missing them to satisfy the coverage threshold.
Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts
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Under Strict Mode one transfer was minted; the hook stayed preparing through the proxied redeem page and turned ready when the destination loaded signed in.
Also checked · 4 match · 1 differs · 1 not run
Failed redeem reports its code; retry recovers Signed in on a real device · Blocked FAPI refusal passes through unchanged Transfer URL hidden from logs Android browser intent carries REFERRER_NAME Hosted auth unchanged by refactor
Warning
Doesn't do what was asked
Failed redeem reports its code; retry recovers
Both status values gave error expired and retry() minted a second URL that ended ready and signed in; but when the failed page's onLoadEnd lands after retry's new props, the new attempt stays error expired even after the WebView signs in (2 of ~10 natural runs, reproduced determi...
Proof on 09a44a3d · mocked: Clerk Frontend API session_transfers (setting session transfers instance flag), react-native-webview (No iOS simulator here; a Playwright Chromium page loads the URL and forwards its...), expo-intent-launcher (No Android emulator; a recording stub captures startActivityAsync arguments) · not run: iOS simulator / Android emulator (Linux sandbox has no iOS Simulator, and no instance here has session transfers e...) · Did Proof get it right? Yes · No
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Failed pre-merge checks:
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Write docstrings for the functions missing them to satisfy the coverage
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Description
A signed-in Expo app can now open a web page that is already signed in as the same user. The page can open in a WebView the app renders or in the system browser. The SDK asks Clerk for a one-time sign-in URL, which is valid for 60 seconds, right before it opens the page. FAPI's
session_transfersendpoints are live behind a per-instance flag.@clerk/expo/native-to-webhas three exports.useAuthenticatedWebView({ destination })prepares the URL when the screen mounts. It returnswebViewPropsto spread onto areact-native-webview<WebView>, and astatusofpreparing,ready,signed-out, orerror.statusstayspreparingwhile the WebView is on Clerk's "Signing you in" page, so the app can keep its own overlay up until the destination loads. The hook matches the redeem page by origin and path, so it also works for instances behind a proxy. If redeem fails, the hook reads__clerk_error_codefrom the landing URL and reports it aserror.code. It accepts both the current__clerk_status=failedandsession_transfer_failed, which clerk_go #23983 changes it to.useNativeToWeb().openExternalBrowser({ destination })opens the default browser. iOS usesLinking.openURL. Android Chrome refuses an app-opened URL unless the intent names the app as referrer. On Android the opener starts a VIEW intent throughexpo-intent-launcher, with the String extraandroid.intent.extra.REFERRER_NAMEset toandroid-app://<package>. Chrome ignores a StringEXTRA_REFERRER, but it turnsREFERRER_NAMEintoReferer: android-app://<package>/. That means@clerk/exponeeds no native code of its own.isSessionTransferError(error). Every failure is anError & { code }. FAPI refusal codes and redeem codes pass through unchanged, and theClerkAPIResponseErrorstays oncause.@clerk/expo/native-to-web/advancedexportsprepareSessionTransfer({ destination, presentation })for apps that present the URL themselves. Theurlproperty of the returned object is not enumerable, soconsole.logandJSON.stringifyleave it out.React Strict Mode and remounts don't create a second live transfer. A module-level ledger hands an in-flight or unused transfer to the next presenter that asks for the same session and destination. A transfer is marked used as soon as its URL reaches a WebView or the browser.
The first commit moves the FAPI request helpers from
utils/hostedAuth.tstoutils/fapiRequest.ts, andgetExpoAppIdentifierfromuseHostedAuth.tstoutils/appIdentifier.ts. Hosted auth now uses the shared copies. Its behavior doesn't change and its tests are unchanged.expo-intent-launcheris a new optional peer.react-native-webviewis a devDependency for a type test only. Its props are typed structurally, so it is not a peer.I ran it with an Expo SDK 58 app against a development instance that has the flag on, on an iPhone 18 Pro simulator (iOS 27) and an Android API 36 emulator with Chrome. Each path below ended signed in:
useAuthenticatedWebViewreadyreadyopenExternalBrowserREFERRER_NAME, signed inerror: expired,retry()signs inerror: expired,retry()signs inThere is one known gap. On iOS,
onLoadEndfor the destination fires before WebKit paints the new page. When the overlay drops, the "Signing you in" page shows for one frame, about 33 ms, then the destination paints. Android didn't show this.Checklist
pnpm testruns as expected.pnpm buildruns as expected.Type of change
🤖 Generated with Claude under Rob's supervision.
Part of MOBILE-450