AI Security: How AI assistants securely assess your personal data

The AI processes the returned data and presents it as a natural language response inside the chat interface.

Building the Same Flow in a Custom Chatbot

Now let's see how a custom chatbot can implement the same approach using C#.

Step 1: Create an Authentication Service

Create a new class named AiAssistantAuthService.

Inside it, add a method named:

GetCalendarTokenOnBehalfOfUserAsync

Step 2: Register Your Application

Go to your Identity Provider's application registration portal, such as:

• Microsoft Entra ID

• Google Cloud

• Facebook

• Other OAuth providers

Register a new application for your AI Assistant.

Step 3: Configure the Identity Client

Create a confidential client using:

• Tenant ID

• Client ID

• Client Secret

Use the user's existing access token (which the chatbot already possesses after login).

Most importantly, specify the required OAuth scopes, which define exactly what the AI is allowed to do.

Step 4: Request an OBO Token

Send the authenticated user's token to the Identity Provider and request an On-Behalf-Of access token.

Sample Code

using Microsoft.Identity.Client;

public class AiAssistantAuthService
{
    private readonly string clientId = "YOURAI_ASSISTANT_CLIENT_ID";
    private readonly string clientSecret = "YOURAI_ASSISTANT_CLIENT_SECRET";
    private readonly string tenantId = "YOURORGANIZATION_TENANT_ID";

    public async Task<string> GetCalendarTokenOnBehalfOfUserAsync(string incomingUserToken)
    {
        string authority = $"https://login.microsoftonline.com/{tenantId}";

        IConfidentialClientApplication app =
            ConfidentialClientApplicationBuilder.Create(clientId)
                .WithClientSecret(clientSecret)
                .WithAuthority(new Uri(authority))
                .Build();

        string[] scopes =
        {
            "https://graph.microsoft.com/Calendars.Read"
        };

        UserAssertion userAssertion = new UserAssertion(incomingUserToken);

        try
        {
            AuthenticationResult result =
                await app.AcquireTokenOnBehalfOf(scopes, userAssertion)
                         .ExecuteAsync();

            return result.AccessToken;
        }
        catch (MsalServiceException ex)
        {
            Console.WriteLine($"Error during OBO token exchange: {ex.Message}");
            throw;
        }
    }
}

Using the Generated OBO Token

After successfully generating the OBO token, the AI Assistant includes it in the Authorization header while calling APIs that expose personal data, such as:

• Email

• Calendar

• Contacts

• Files

The AI Assistant can then access only the resources and operations permitted by the token's assigned scope.

Why This Approach Is Secure

Using the OAuth 2.0 On-Behalf-Of flow provides multiple security benefits:

• The AI never stores or knows the user's password.

• The AI can never access data that the authenticated user cannot access.

• Every API call is performed using a short-lived access token.

• Permissions are limited to the requested scope.

• Corporate security teams can audit every operation performed on behalf of the user.

• Access can be revoked immediately by the Identity Provider without changing user credentials.

Summary

OAuth 2.0 On-Behalf-Of (OBO) Token Delegation enables AI assistants to securely access user resources without exposing passwords or granting unrestricted permissions. Instead of impersonating users directly, the AI exchanges the user's existing access token for a temporary, scoped token that is limited to specific APIs and permissions. This approach ensures least-privilege access, supports enterprise auditing, and allows AI assistants to safely interact with personal data such as calendars, emails, and files while maintaining strong security boundaries.