feat(auth): add WorkOS and Keycloak SSO providers

apps/web/src/app/auth/provider/[provider]/page.tsx

@@ -0,0 +1,77 @@
+'use client';
+
+import Link from 'next/link';
+import { useEffect, useState } from 'react';
+import { useParams, useSearchParams } from 'next/navigation';
+import { signIn } from '@/lib/auth-client';
+import { getSsoProvider } from '@/lib/sso-providers';
+
+export default function AuthProviderRedirectPage(): React.ReactElement {
+  const params = useParams<{ provider: string }>();
+  const searchParams = useSearchParams();
+  const providerId = typeof params.provider === 'string' ? params.provider : '';
+  const provider = getSsoProvider(providerId);
+  const callbackURL = searchParams.get('callbackURL') ?? '/chat';
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    const currentProvider = provider;
+
+    if (!currentProvider) {
+      setError('Unknown SSO provider.');
+      return;
+    }
+
+    if (!currentProvider.enabled) {
+      setError(`${currentProvider.buttonLabel} is not enabled in this deployment.`);
+      return;
+    }
+
+    const activeProvider = currentProvider;
+    let cancelled = false;
+
+    async function redirectToProvider(): Promise<void> {
+      const result = await signIn.oauth2({
+        providerId: activeProvider.id,
+        callbackURL,
+      });
+
+      if (!cancelled && result?.error) {
+        setError(result.error.message ?? `${activeProvider.buttonLabel} sign in failed.`);
+      }
+    }
+
+    void redirectToProvider();
+
+    return () => {
+      cancelled = true;
+    };
+  }, [callbackURL, provider]);
+
+  return (
+    <div className="mx-auto flex min-h-[50vh] max-w-md flex-col justify-center">
+      <h1 className="text-2xl font-semibold text-text-primary">Single sign-on</h1>
+      <p className="mt-2 text-sm text-text-secondary">
+        {provider
+          ? `Redirecting you to ${provider.buttonLabel.replace('Continue with ', '')}...`
+          : 'Preparing your sign-in request...'}
+      </p>
+
+      {error ? (
+        <div className="mt-6 rounded-lg border border-error/30 bg-error/10 px-4 py-3 text-sm text-error">
+          <p>{error}</p>
+          <Link
+            href="/login"
+            className="mt-3 inline-block font-medium text-blue-400 hover:text-blue-300"
+          >
+            Return to login
+          </Link>
+        </div>
+      ) : (
+        <div className="mt-6 rounded-lg border border-surface-border bg-surface-elevated px-4 py-3 text-sm text-text-secondary">
+          If the redirect does not start automatically, return to the login page and try again.
+        </div>
+      )}
+    </div>
+  );
+}