From de231e03e5e1aeded9f91f8cbf497aef0eb07a69 Mon Sep 17 00:00:00 2001
From: Jacek <jacek@clerk.dev>
Date: Wed, 3 Sep 2025 21:44:21 -0500
Subject: [PATCH 1/4] fix(clerk-js): Remove double slash from FAPI client urls

---
 .../src/core/__tests__/fapiClient.spec.ts     | 21 +++++++++++++++++++
 packages/clerk-js/src/core/fapiClient.ts      |  6 +++++-
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/packages/clerk-js/src/core/__tests__/fapiClient.spec.ts b/packages/clerk-js/src/core/__tests__/fapiClient.spec.ts
index 728b259fe94..7aa96b3368f 100644
--- a/packages/clerk-js/src/core/__tests__/fapiClient.spec.ts
+++ b/packages/clerk-js/src/core/__tests__/fapiClient.spec.ts
@@ -21,6 +21,13 @@ const fapiClientWithProxy = createFapiClient({
   proxyUrl,
 });
 
+const proxyUrlWithTrailingSlash = 'https://clerk.com/api/__clerk/';
+
+const fapiClientWithProxyTrailingSlash = createFapiClient({
+  ...baseFapiClientOptions,
+  proxyUrl: proxyUrlWithTrailingSlash,
+});
+
 type RecursivePartial<T> = {
   [P in keyof T]?: RecursivePartial<T[P]>;
 };
@@ -79,6 +86,20 @@ describe('buildUrl(options)', () => {
     );
   });
 
+  it('returns the correct URL when proxy URL has a trailing slash', () => {
+    // The expected URL should NOT have double slashes after __clerk
+    expect(fapiClientWithProxyTrailingSlash.buildUrl({ path: '/foo' }).href).toBe(
+      `https://clerk.com/api/__clerk/v1/foo?__clerk_api_version=${SUPPORTED_FAPI_VERSION}&_clerk_js_version=test`,
+    );
+  });
+
+  it('handles complex paths correctly with proxy URL with trailing slash', () => {
+    const path = '/client/sign_ins/sia_123/prepare_first_factor';
+    expect(fapiClientWithProxyTrailingSlash.buildUrl({ path }).href).toBe(
+      `https://clerk.com/api/__clerk/v1${path}?__clerk_api_version=${SUPPORTED_FAPI_VERSION}&_clerk_js_version=test`,
+    );
+  });
+
   it('uses domain from options if production', () => {
     expect(
       createFapiClient({ ...baseFapiClientOptions, domain: 'clerk.other.com', instanceType: 'production' }).buildUrl({
diff --git a/packages/clerk-js/src/core/fapiClient.ts b/packages/clerk-js/src/core/fapiClient.ts
index d12cce9a181..79939740a18 100644
--- a/packages/clerk-js/src/core/fapiClient.ts
+++ b/packages/clerk-js/src/core/fapiClient.ts
@@ -149,7 +149,11 @@ export function createFapiClient(options: FapiClientOptions): FapiClient {
 
     if (options.proxyUrl) {
       const proxyBase = new URL(options.proxyUrl);
-      const proxyPath = proxyBase.pathname.slice(1, proxyBase.pathname.length);
+      // Remove leading slash and any trailing slash from the proxy pathname
+      let proxyPath = proxyBase.pathname.slice(1);
+      if (proxyPath.endsWith('/')) {
+        proxyPath = proxyPath.slice(0, -1);
+      }
       return buildUrlUtil(
         {
           base: proxyBase.origin,

From a7151133cb328bd2627c7eca86d4298f1e4aa3ad Mon Sep 17 00:00:00 2001
From: Jacek <jacek@clerk.dev>
Date: Wed, 3 Sep 2025 21:45:00 -0500
Subject: [PATCH 2/4] wip

---
 packages/clerk-js/src/core/fapiClient.ts | 1 -
 1 file changed, 1 deletion(-)

diff --git a/packages/clerk-js/src/core/fapiClient.ts b/packages/clerk-js/src/core/fapiClient.ts
index 79939740a18..2207aca0251 100644
--- a/packages/clerk-js/src/core/fapiClient.ts
+++ b/packages/clerk-js/src/core/fapiClient.ts
@@ -149,7 +149,6 @@ export function createFapiClient(options: FapiClientOptions): FapiClient {
 
     if (options.proxyUrl) {
       const proxyBase = new URL(options.proxyUrl);
-      // Remove leading slash and any trailing slash from the proxy pathname
       let proxyPath = proxyBase.pathname.slice(1);
       if (proxyPath.endsWith('/')) {
         proxyPath = proxyPath.slice(0, -1);

From 03a2171a2a8272c6c497d73cc2c148780f07f346 Mon Sep 17 00:00:00 2001
From: Jacek <jacek@clerk.dev>
Date: Wed, 3 Sep 2025 21:57:29 -0500
Subject: [PATCH 3/4] changeset

---
 .changeset/fluffy-comics-peel.md | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changeset/fluffy-comics-peel.md

diff --git a/.changeset/fluffy-comics-peel.md b/.changeset/fluffy-comics-peel.md
new file mode 100644
index 00000000000..510c43dd7c0
--- /dev/null
+++ b/.changeset/fluffy-comics-peel.md
@@ -0,0 +1,5 @@
+---
+'@clerk/clerk-js': patch
+---
+
+Fixing an issue where an incorrect FAPI client URLs were generated in an app using a proxy configuration.

From 418b448fd01943a0e92e8e6cccf84c2e452e393d Mon Sep 17 00:00:00 2001
From: Jacek Radko <jacek@clerk.dev>
Date: Wed, 3 Sep 2025 22:05:12 -0500
Subject: [PATCH 4/4] Update .changeset/fluffy-comics-peel.md

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>
---
 .changeset/fluffy-comics-peel.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.changeset/fluffy-comics-peel.md b/.changeset/fluffy-comics-peel.md
index 510c43dd7c0..8531c19d220 100644
--- a/.changeset/fluffy-comics-peel.md
+++ b/.changeset/fluffy-comics-peel.md
@@ -2,4 +2,4 @@
 '@clerk/clerk-js': patch
 ---
 
-Fixing an issue where an incorrect FAPI client URLs were generated in an app using a proxy configuration.
+Fix double slash in FAPI client URLs when using a proxy configuration (avoids 308 redirects).