fix: add PKCE support for Logto auth and fix Traefik routing

Logto requires PKCE (Proof Key for Code Exchange) for SPA auth.
Added code_challenge/code_verifier to login and callback flow.

Also fixed Traefik router-service linking — when a container defines
multiple routers, each needs an explicit service binding or Traefik
v3 refuses to auto-link them.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/auth/CallbackPage.tsx

@@ -3,6 +3,7 @@ import { useNavigate } from 'react-router';
 import { useAuthStore } from './auth-store';
 import { Spinner } from '@cameleer/design-system';
 import { fetchConfig } from '../config';
+import { getCodeVerifier } from './pkce';
 
 export function CallbackPage() {
   const navigate = useNavigate();
@@ -16,6 +17,12 @@ export function CallbackPage() {
       return;
     }
 
+    const codeVerifier = getCodeVerifier();
+    if (!codeVerifier) {
+      navigate('/login');
+      return;
+    }
+
     const redirectUri = `${window.location.origin}/callback`;
 
     fetchConfig().then((config) => {
@@ -27,6 +34,7 @@ export function CallbackPage() {
           code,
           client_id: config.logtoClientId,
           redirect_uri: redirectUri,
+          code_verifier: codeVerifier,
         }),
       })
         .then((r) => r.json())

ui/src/auth/LoginPage.tsx

@@ -1,6 +1,7 @@
 import { useEffect, useState } from 'react';
 import { Button, Spinner } from '@cameleer/design-system';
 import { fetchConfig } from '../config';
+import { generatePkce, storeCodeVerifier } from './pkce';
 
 export function LoginPage() {
   const [config, setConfig] = useState<{ logtoEndpoint: string; logtoClientId: string } | null>(null);
@@ -21,14 +22,18 @@ export function LoginPage() {
     );
   }
 
-  const handleLogin = () => {
+  const handleLogin = async () => {
     if (!config?.logtoClientId) return;
+    const { codeVerifier, codeChallenge } = await generatePkce();
+    storeCodeVerifier(codeVerifier);
     const redirectUri = `${window.location.origin}/callback`;
     const params = new URLSearchParams({
       client_id: config.logtoClientId,
       redirect_uri: redirectUri,
       response_type: 'code',
       scope: 'openid profile email offline_access',
+      code_challenge: codeChallenge,
+      code_challenge_method: 'S256',
     });
     window.location.href = `${config.logtoEndpoint}/oidc/auth?${params}`;
   };

ui/src/auth/pkce.ts

@@ -0,0 +1,38 @@
+const VERIFIER_KEY = 'pkce_code_verifier';
+
+function generateRandomString(length: number): string {
+  const array = new Uint8Array(length);
+  crypto.getRandomValues(array);
+  return Array.from(array, (b) => b.toString(16).padStart(2, '0')).join('').slice(0, length);
+}
+
+async function sha256(plain: string): Promise<ArrayBuffer> {
+  const encoder = new TextEncoder();
+  return crypto.subtle.digest('SHA-256', encoder.encode(plain));
+}
+
+function base64UrlEncode(buffer: ArrayBuffer): string {
+  const bytes = new Uint8Array(buffer);
+  let binary = '';
+  for (const b of bytes) {
+    binary += String.fromCharCode(b);
+  }
+  return btoa(binary).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
+}
+
+export async function generatePkce(): Promise<{ codeVerifier: string; codeChallenge: string }> {
+  const codeVerifier = generateRandomString(64);
+  const hashed = await sha256(codeVerifier);
+  const codeChallenge = base64UrlEncode(hashed);
+  return { codeVerifier, codeChallenge };
+}
+
+export function storeCodeVerifier(verifier: string): void {
+  sessionStorage.setItem(VERIFIER_KEY, verifier);
+}
+
+export function getCodeVerifier(): string | null {
+  const verifier = sessionStorage.getItem(VERIFIER_KEY);
+  sessionStorage.removeItem(VERIFIER_KEY);
+  return verifier;
+}