diff --git a/src/lib/create-config.ts b/src/lib/create-config.ts
index e81f23df24..9244458cab 100644
--- a/src/lib/create-config.ts
+++ b/src/lib/create-config.ts
@@ -15,6 +15,7 @@ import {
     IListeningHost,
 } from './types/option';
 import { getDefaultLogProvider, LogLevel, validateLogProvider } from './logger';
+import { defaultCustomAuthDenyAll } from './default-custom-auth-deny-all';
 
 const safeToUpper = (s: string) => (s ? s.toUpperCase() : s);
 
@@ -98,7 +99,7 @@ const defaultVersionOption: IVersionOption = {
 const defaultAuthentication: IAuthOption = {
     enableApiToken: safeBoolean(process.env.AUTH_ENABLE_API_TOKEN, true),
     type: authTypeFromString(process.env.AUTH_TYPE),
-    customAuthHandler: () => {},
+    customAuthHandler: defaultCustomAuthDenyAll,
     createAdminUser: true,
 };
 
@@ -125,6 +126,16 @@ const dbPort = (dbConfig: Partial<IDBOption>): Partial<IDBOption> => {
     return dbConfig;
 };
 
+const removeUndefinedKeys = (o: object): object =>
+    Object.keys(o).reduce((a, key) => {
+        if (o[key] !== undefined) {
+            // eslint-disable-next-line no-param-reassign
+            a[key] = o[key];
+            return a;
+        }
+        return a;
+    }, {});
+
 export function createConfig(options: IUnleashOptions): IUnleashConfig {
     let extraDbOptions = {};
     if (options.databaseUrl) {
@@ -160,7 +171,9 @@ export function createConfig(options: IUnleashOptions): IUnleashConfig {
 
     const authentication: IAuthOption = mergeAll([
         defaultAuthentication,
-        options.authentication,
+        options.authentication
+            ? removeUndefinedKeys(options.authentication)
+            : options.authentication,
     ]);
 
     const { ui } = options;
diff --git a/src/lib/default-custom-auth-deny-all.ts b/src/lib/default-custom-auth-deny-all.ts
new file mode 100644
index 0000000000..ab4e812df2
--- /dev/null
+++ b/src/lib/default-custom-auth-deny-all.ts
@@ -0,0 +1,18 @@
+import { IUnleashConfig } from './types/option';
+
+const customAuthWarning =
+    'You have to configure a custom authentication middleware. Read https://docs.getunleash.io/docs/deploy/configuring_unleash for more details';
+
+export function defaultCustomAuthDenyAll(
+    // eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
+    app: any,
+    config: IUnleashConfig,
+): void {
+    const logger = config.getLogger('src/lib/app/customAuthHandler');
+    app.use(`${config.server.baseUriPath}/api`, async (req, res) => {
+        logger.error(customAuthWarning);
+        res.status(401).send({
+            error: customAuthWarning,
+        });
+    });
+}
diff --git a/src/test/e2e/custom-auth.test.ts b/src/test/e2e/custom-auth.test.ts
new file mode 100644
index 0000000000..b3bdfd3716
--- /dev/null
+++ b/src/test/e2e/custom-auth.test.ts
@@ -0,0 +1,32 @@
+import test, { before } from 'ava';
+
+import dbInit from './helpers/database-init';
+import { setupAppWithCustomAuth } from './helpers/test-helper';
+
+let db;
+let stores;
+
+before(async () => {
+    db = await dbInit('custom_auth_serial');
+    stores = db.stores;
+});
+
+test('Using custom auth type without defining custom middleware causes default DENY ALL policy to take effect', async t => {
+    t.plan(1);
+    const request = await setupAppWithCustomAuth(stores, undefined);
+    await request
+        .get('/api/admin/features')
+        .expect(401)
+        .expect(res => {
+            t.is(
+                res.body.error,
+                'You have to configure a custom authentication middleware. Read https://docs.getunleash.io/docs/deploy/configuring_unleash for more details',
+            );
+        });
+});
+
+test('If actually configuring a custom middleware should configure the middleware', async t => {
+    t.plan(0);
+    const request = await setupAppWithCustomAuth(stores, () => {});
+    return request.get('/api/admin/features').expect(200);
+});