diff --git a/src/routes/irma/[...path]/+server.ts b/src/routes/irma/[...path]/+server.ts
index 649bf80..0324fc9 100644
--- a/src/routes/irma/[...path]/+server.ts
+++ b/src/routes/irma/[...path]/+server.ts
@@ -1,7 +1,13 @@
+import { error } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
 import { YIVI_SERVER_URL, YIVI_SERVER_TOKEN } from '$lib/server/auth/yivi';
+import { isAllowed } from './allowlist';
 
 const handler: RequestHandler = async ({ params, request }) => {
+	if (!isAllowed(params.path)) {
+		error(403, 'Forbidden');
+	}
+
 	const url = `${YIVI_SERVER_URL}/${params.path}`;
 
 	const headers: Record<string, string> = {};
diff --git a/src/routes/irma/[...path]/allowlist.ts b/src/routes/irma/[...path]/allowlist.ts
new file mode 100644
index 0000000..1b249ab
--- /dev/null
+++ b/src/routes/irma/[...path]/allowlist.ts
@@ -0,0 +1,13 @@
+// The Yivi frontend SDK only talks to /irma/session[...]. Everything else is
+// either administrative (e.g. /scheme, /configuration) or unknown territory
+// on the upstream Yivi server and must not be proxied with the server's
+// auth token.
+export const ALLOWED_PREFIXES = ['session'];
+
+export function isAllowed(path: string | undefined): boolean {
+	if (!path) return false;
+	// Reject path traversal attempts outright.
+	if (path.includes('..')) return false;
+	const firstSegment = path.split('/')[0];
+	return ALLOWED_PREFIXES.includes(firstSegment);
+}
diff --git a/tests/unit/irma-proxy-allowlist.test.ts b/tests/unit/irma-proxy-allowlist.test.ts
new file mode 100644
index 0000000..121eca2
--- /dev/null
+++ b/tests/unit/irma-proxy-allowlist.test.ts
@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest';
+import { isAllowed } from '../../src/routes/irma/[...path]/allowlist';
+
+describe('irma proxy path allowlist', () => {
+	it('allows the session prefix', () => {
+		expect(isAllowed('session')).toBe(true);
+	});
+
+	it('allows session subpaths', () => {
+		expect(isAllowed('session/abc123')).toBe(true);
+		expect(isAllowed('session/abc123/status')).toBe(true);
+	});
+
+	it('rejects unknown top-level prefixes', () => {
+		expect(isAllowed('admin')).toBe(false);
+		expect(isAllowed('scheme')).toBe(false);
+		expect(isAllowed('configuration')).toBe(false);
+		expect(isAllowed('keyshare')).toBe(false);
+	});
+
+	it('rejects path traversal attempts', () => {
+		expect(isAllowed('session/../admin')).toBe(false);
+		expect(isAllowed('../admin')).toBe(false);
+		expect(isAllowed('session/..')).toBe(false);
+	});
+
+	it('rejects empty and undefined paths', () => {
+		expect(isAllowed('')).toBe(false);
+		expect(isAllowed(undefined)).toBe(false);
+	});
+
+	it('does not allow prefix-spoofing like sessionadmin', () => {
+		expect(isAllowed('sessionadmin')).toBe(false);
+		expect(isAllowed('sessionfoo/bar')).toBe(false);
+	});
+});