Direct Line enhanced authentication


This article describes potential security risks when users connect to a bot, for example using the Web Chat control. Also, it shows mitigating solutions using the Direct Line enhanced authentication settings and secure user ID handling.

There are two user identities:

  • The channel user's identity. An attacker can use it for Impersonation.
  • The user's identity from the identity provider that the bot uses to authenticate the user. An attacker can use it for Identity spoofing.


Impersonation refers to the action of an attacker who makes the bot think that they're someone else. For example, in Web Chat, the attacker can impersonate someone else by changing the user ID of the Web Chat instance.

Impersonation mitigation

  • Make the user ID unguessable.

  • Connect a bot to Direct Line.

  • Enable the Direct Line channel's enhanced authentication option to allow the Azure AI Bot Service to further detect and reject any user ID change. This means the user ID (Activity.From.Id) on messages from Direct Line to the bot will always be the same as the one you used to initialize the Web Chat control.


    Direct Line creates a token based on the Direct Line secret and embeds the User.Id in the token. It assures that the messages sent to the bot have that User.Id as the activity's From.Id. If a client sends a message to Direct Line having a different From.Id, it will be changed to the ID embedded in the token before forwarding the message to the bot. So you can't use another user ID after a channel secret is initialized with that ID.

    This feature requires the user ID to start with dl_ as shown below.


    For a regional bot, set dlUrl according to the selected region.
    If selected europe, set "".
    If selected india, set "".
    For more information about regional bots, see Regionalization in Azure AI Bot Service.

    public class HomeController : Controller
        private const string secret = "<TODO: DirectLine secret>";
        private const string dlUrl = "";
        public async Task<ActionResult> Index()
            HttpClient client = new HttpClient();
            var userId = $"dl_{Guid.NewGuid()}";
            HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, dlUrl);
            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", secret);
            request.Content = new StringContent(
                    new { User = new { Id = userId } }),
            var response = await client.SendAsync(request);
            string token = String.Empty;
            if (response.IsSuccessStatusCode)
                var body = await response.Content.ReadAsStringAsync();
                token = JsonConvert.DeserializeObject<DirectLineToken>(body).token;
            var config = new ChatConfig()
                Token = token,
                UserId = userId
            return View(config);

    The generated token, based on the Direct Line secret, is then used in the Web Chat control as shown below:

    @model Bot_Auth_DL_Secure_Site_MVC.Models.ChatConfig
        ViewData["Title"] = "Home Page";
    <div id="webchat" role="main" />
        <script src=""></script>
              directLine: window.WebChat.createDirectLine({ token: '@Model.Token' }),
                userID: '@Model.UserId'
          }, document.getElementById('webchat'));

Identity spoofing

Identity spoofing refers to the action of an attacker that assumes the identity of a legitimate user and then uses that identity to accomplish a malicious goal.

When a bot asks the channel user A to sign-in to an identity provider, the sign-in process must assure that user A is the only one that signs into the provider. If another user is also allowed to sign-in the provider, they would have access to user A resources through the bot.

User identity spoofing mitigation

In the Web Chat control, there are two mechanisms to assure that the proper user is signed in.

  1. Magic code. At the end of the sign-in process, the user is presented with a randomly generated 6-digit code (magic code). The user must type this code in the conversation to complete the sign-in process. This tends to result in a bad user experience. Additionally, it's susceptible to phishing attacks; a malicious user can trick another user to sign-in and obtain the magic code.

  2. Direct Line enhanced authentication. Use Direct Line enhanced authentication to guarantee that the sign-in process can only be completed in the same browser session as the Web Chat client.

    To enable this protection, start Web Chat with a Direct Line token that contains a list of trusted domains that can host the bot's Web Chat client. With enhanced authentication options, you can statically specify the trusted domains (trusted origins) list in the Direct Line configuration page. See the Configure enhanced authentication section.