fix: discover OIDC metadata server-side to avoid CORS failures #382

app/(main)/[locale]/login/page.tsx

@@ -14,7 +14,7 @@ import { useConfig } from "@/hooks/use-config";
 import { apiFetch, getPathPrefix, withBasePath } from "@/lib/browser-navigation";
 import { cn } from "@/lib/utils";
 import { AlertCircle, Loader2, X, Info, Eye, EyeOff, LogIn, Sun, Moon, Monitor, Check, Shield, Play, Copy } from "lucide-react";
-import { discoverOAuth, type OAuthMetadata } from "@/lib/oauth/discovery";
+import { type OAuthMetadata } from "@/lib/oauth/discovery";
 import { generateCodeVerifier, generateCodeChallenge, generateState } from "@/lib/oauth/pkce";
 import { useUpdateStore, selectBanner } from "@/stores/update-store";
 import type { PublicJmapServerEntry } from "@/lib/admin/jmap-servers";
@@ -329,16 +329,27 @@ export default function LoginPage() {
     if (!oauthEnabled || !serverUrl) return;
     setOauthDiscoveryDone(false);
     setOauthMetadata(null);
-    discoverOAuth(effectiveOauthIssuerUrl || serverUrl)
+    const controller = new AbortController();
+    // Discover via our own origin rather than fetching the IdP's /.well-known/*
+    // documents directly from the browser. A direct cross-origin discovery
+    // fetch is subject to CORS, and providers like Authentik serve those
+    // documents without Access-Control-Allow-Origin, so the browser blocks the
+    // response and login breaks (issue #382). The proxy runs discovery server
+    // side where CORS does not apply.
+    const query = selectedServer?.id ? `?server_id=${encodeURIComponent(selectedServer.id)}` : "";
+    apiFetch(`/api/auth/oauth/metadata${query}`, { signal: controller.signal })
+      .then(async (res) => (res.ok ? ((await res.json()) as OAuthMetadata) : null))
       .then((metadata) => {
         setOauthMetadata(metadata);
         setOauthDiscoveryDone(true);
       })
-      .catch(() => {
+      .catch((err) => {
+        if (err?.name === "AbortError") return;
         setOauthMetadata(null);
         setOauthDiscoveryDone(true);
       });
-  }, [oauthEnabled, serverUrl, effectiveOauthIssuerUrl]);
+    return () => controller.abort();
+  }, [oauthEnabled, serverUrl, effectiveOauthIssuerUrl, selectedServer?.id]);
 
   // Auto-SSO: when enabled with OAUTH_ONLY, skip the login page entirely
   const ssoError = searchParams.get("sso_error");

app/api/auth/oauth/metadata/route.ts

@@ -0,0 +1,53 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { logger } from '@/lib/logger';
+import { configManager } from '@/lib/admin/config-manager';
+import { getMetadata, getRequiredConfig } from '@/lib/oauth/token-exchange';
+
+/**
+ * Same-origin OAuth metadata (discovery) proxy.
+ *
+ * The login page needs the authorization_endpoint to build the PKCE authorize
+ * URL in the browser. Discovering it directly from the browser means a
+ * cross-origin fetch to the IdP's /.well-known/* documents, which is subject
+ * to CORS: providers like Authentik serve those documents without an
+ * Access-Control-Allow-Origin header, so the browser blocks the response and
+ * discovery fails (issue #382). Performing discovery here - server to server,
+ * where CORS does not apply - and handing the result back as a same-origin
+ * response sidesteps the problem entirely.
+ *
+ * The discovery URL is resolved from admin config (via server_id), never from
+ * client input, so this cannot be abused as an open SSRF proxy. Endpoint URLs
+ * in the discovered document are still gated by the SSRF validator inside
+ * discoverOAuth. The returned fields are public well-known metadata.
+ */
+export async function GET(request: NextRequest) {
+  await configManager.ensureLoaded();
+  const serverId = request.nextUrl.searchParams.get('server_id');
+
+  let discoveryUrl: string;
+  try {
+    ({ discoveryUrl } = getRequiredConfig(serverId));
+  } catch {
+    // OAuth not configured for this server - surface as "no metadata" rather
+    // than a 500 so the login page just hides the SSO button.
+    return NextResponse.json({ error: 'OAuth not configured' }, { status: 404 });
+  }
+
+  try {
+    const metadata = await getMetadata(serverId);
+    if (!metadata?.authorization_endpoint || !metadata.token_endpoint) {
+      logger.warn('OAuth metadata discovery returned no usable endpoints', { discoveryUrl });
+      return NextResponse.json({ error: 'OAuth discovery failed' }, { status: 502 });
+    }
+    return NextResponse.json(metadata, {
+      // Mirror the in-process discovery cache TTL so repeated login-page loads
+      // hit the CDN/browser cache instead of re-running discovery.
+      headers: { 'Cache-Control': 'private, max-age=600' },
+    });
+  } catch (error) {
+    logger.error('OAuth metadata discovery error', {
+      error: error instanceof Error ? error.message : 'Unknown error',
+    });
+    return NextResponse.json({ error: 'OAuth discovery failed' }, { status: 502 });
+  }
+}