microsoft/ailab · critical · Error

Direct Line secret not defined.

Error message

Direct Line secret not defined.

What it means

The middelware() factory in the DirectLine-to-Actions-on-Google connector requires a Direct Line secret to proxy conversations between Google Assistant and the Bot Framework Direct Line channel. It throws immediately if the secret argument is falsy (undefined, null, or empty string). This is a fail-fast guard: the library cannot authenticate to Direct Line without the secret, so it refuses to set up the Express router.

Solutions

1. Set the Direct Line secret environment variable (e.g. DIRECT_LINE_SECRET=<secret from Direct Line channel in Azure Portal>) before starting the app
2. Pass the secret explicitly as the first argument to middelware(secret) and verify it is non-empty at startup
3. In Azure hosting, add the value to Application Settings / environment configuration for the deployed instance
4. Confirm you are using the Direct Line channel secret (from the Direct Line channel blade), not the bot's MicrosoftAppPassword

Example fix

// before
const { router } = middelware(process.env.DIRECT_LINE_SECRET);
// after
if (!process.env.DIRECT_LINE_SECRET) {
  throw new Error('Set DIRECT_LINE_SECRET env var before starting.');
}
const { router } = middelware(process.env.DIRECT_LINE_SECRET);

if (!process.env.DIRECT_LINE_SECRET) {
  throw new Error('DIRECT_LINE_SECRET env var must be set before calling middelware()');
}

function hasDirectLineSecret(v) {
  return typeof v === 'string' && v.length > 0;
}

let mw;
try {
  mw = middelware(process.env.DIRECT_LINE_SECRET);
} catch (e) {
  if (e.message.includes('Direct Line secret not defined')) {
    console.error('Startup config error: set DIRECT_LINE_SECRET');
    process.exit(1);
  }
  throw e;
}

When it happens

Trigger: Calling middelware() with no argument, with undefined/null, or with an empty string, e.g. middelware(process.env.DIRECT_LINE_SECRET) where that env var is unset.

Common situations: Deploying without setting DIRECT_LINE_SECRET in the environment (local run, Azure App Service slot swap missing app settings, docker env file omitted); passing the Bot Framework app ID/password instead of a Direct Line secret; a typo in the env variable name.

Understand the failure class

Background: "API key is required" / "API key not found" / "No API key was set": the missing-api-key error family across 16 libraries — this error's family across 16 libraries.

Related errors

• [ ] can't be empty.
• A subscription key is required

AI-assisted analysis of microsoft/ailab@89fe2fc620 (2026-09-13). Data as JSON: /api/errors/26a88810a5d465c7. Report an issue: GitHub.

Appendix: source

Thrown at GoogleAssistantConnector/GoogleAssistant/DirectLineToActionsOnGoogleLib/index.js:14

'use strict';
//=========================================================
// Import modules
//=========================================================
const fulfilment = require('./lib/fulfilment');
const express = require('express');
const bodyParser = require('body-parser');

const router = express.Router();

let middelware = (directlineSecret, messagesObj = null) => {

    if (!directlineSecret) {
        throw new Error('Direct Line secret not defined.');
    }

    router.use(bodyParser.json());
    fulfilment(directlineSecret, messagesObj, router);

    return { router };
};


module.exports = middelware;

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