From 7cc34ceb0b9515936ca74a8c60fac0c71f6da790 Mon Sep 17 00:00:00 2001
From: Yunxiao Xu <xuyunxiao2001@gmail.com>
Date: Wed, 18 Feb 2026 13:52:02 -0800
Subject: [PATCH] feat(frontend): Implement reactive refresh interceptor

---
 frontend/src/services/api.ts       | 75 ++++++++++++++++++++++++++----
 frontend/src/services/auth.test.ts | 15 ++++++
 2 files changed, 80 insertions(+), 10 deletions(-)

diff --git a/frontend/src/services/api.ts b/frontend/src/services/api.ts
index f42744d..1f91170 100644
--- a/frontend/src/services/api.ts
+++ b/frontend/src/services/api.ts
@@ -1,4 +1,4 @@
-import axios from "axios"
+import axios, { type InternalAxiosRequestConfig } from "axios"
 
 const API_URL = import.meta.env.VITE_API_URL || ""
 
@@ -7,27 +7,82 @@ const api = axios.create({
   withCredentials: true, // Crucial for HttpOnly cookies
 })
 
-// Optional callback for unauthorized errors
+// Optional callback for unauthorized errors (fallback if refresh fails)
 let onUnauthorized: (() => void) | null = null
 
 export const registerUnauthorizedCallback = (callback: () => void) => {
   onUnauthorized = callback
 }
 
+// State to manage multiple concurrent refreshes
+let isRefreshing = false
+let refreshSubscribers: ((token: string) => void)[] = []
+
+const subscribeTokenRefresh = (callback: (token: string) => void) => {
+  refreshSubscribers.push(callback)
+}
+
+const onRefreshed = (token: string) => {
+  refreshSubscribers.forEach((callback) => callback(token))
+  refreshSubscribers = []
+}
+
 // Add a response interceptor to handle 401s
 api.interceptors.response.use(
   (response) => response,
-  (error) => {
-    // Only handle if it's not an auth endpoint
-    // This prevents loops during bootstrap and allows login form to show errors
-    const isAuthEndpoint = /^\/auth\//.test(error.config?.url)
+  async (error) => {
+    const originalRequest = error.config as InternalAxiosRequestConfig & { _retry?: boolean }
     
-    if (error.response?.status === 401 && !isAuthEndpoint) {
-      // Unauthorized - session likely expired on a protected data route
-      if (onUnauthorized) {
-        onUnauthorized()
+    // Only handle 401 if it's not already a retry and not an auth endpoint
+    // We allow /auth/login and /auth/register to fail normally to show errors
+    const isAuthEndpoint = /^\/auth\/(login|register|oidc\/callback)/.test(originalRequest.url || "")
+    const isRefreshEndpoint = /^\/auth\/refresh/.test(originalRequest.url || "")
+    
+    if (error.response?.status === 401 && !isAuthEndpoint && !isRefreshEndpoint && !originalRequest._retry) {
+      if (isRefreshing) {
+        // Wait for the current refresh to complete
+        return new Promise((resolve) => {
+          subscribeTokenRefresh((token) => {
+            // Re-run the original request
+            resolve(api(originalRequest))
+          })
+        })
+      }
+
+      originalRequest._retry = true
+      isRefreshing = true
+
+      try {
+        console.log("Reactive refresh: Access token expired, attempting to refresh...")
+        // Call refresh endpoint
+        const response = await api.post("/auth/refresh")
+        const { access_token } = response.data
+        
+        isRefreshing = false
+        onRefreshed(access_token)
+        
+        // Retry the original request
+        return api(originalRequest)
+      } catch (refreshError) {
+        isRefreshing = false
+        refreshSubscribers = []
+        console.error("Reactive refresh failed:", refreshError)
+        
+        // Final failure - session is dead
+        if (onUnauthorized) {
+          onUnauthorized()
+        }
+        return Promise.reject(refreshError)
       }
     }
+    
+    // If it's the refresh endpoint itself failing with 401, trigger logout
+    if (error.response?.status === 401 && isRefreshEndpoint) {
+        if (onUnauthorized) {
+            onUnauthorized()
+        }
+    }
+
     return Promise.reject(error)
   }
 )
diff --git a/frontend/src/services/auth.test.ts b/frontend/src/services/auth.test.ts
index c11d08d..2039f3e 100644
--- a/frontend/src/services/auth.test.ts
+++ b/frontend/src/services/auth.test.ts
@@ -83,4 +83,19 @@ describe("AuthService", () => {
     await AuthService.logout()
     expect(mockedApi.post).toHaveBeenCalledWith("/auth/logout")
   })
+
+  it("successfully refreshes session", async () => {
+    const mockResponse = {
+      data: {
+        access_token: "new-fake-token",
+        token_type: "bearer",
+      },
+    }
+    mockedApi.post.mockResolvedValueOnce(mockResponse)
+
+    const result = await AuthService.refreshSession()
+
+    expect(mockedApi.post).toHaveBeenCalledWith("/auth/refresh")
+    expect(result.access_token).toBe("new-fake-token")
+  })
 })