Microsoft.Teams.Core 1.0.2

Microsoft.Teams.Core

The foundational .NET library for building Microsoft Teams bots. It implements the Activity Protocol, providing the core bot application framework, conversation client, user token client, middleware pipeline, and support for both Bot and Agentic identities.

Key Features

• Activity Processing — Receive, deserialize, and dispatch activities through a middleware pipeline
• Conversation Client — Send, update, and delete activities; manage conversation members and metadata
• User Token Client — OAuth token management, sign-in flows, and token exchange (SSO)
• Middleware Pipeline — Extensible ITurnMiddleware chain for cross-cutting concerns
• Flexible Authentication — Client secrets, managed identities (system/user-assigned), federated identities, and agentic (user-delegated) tokens via MSAL
• Extensible Schema — Loose CoreActivity model with JsonExtensionData for channel-specific properties
• AOT-Compatible — Source-generated JSON serialization via CoreActivityJsonContext

Installation

dotnet add package Microsoft.Teams.Core

Quick Start

Register Services & Map Endpoint

var builder = WebApplication.CreateBuilder(args);
builder.AddBotApplication();

var app = builder.Build();
var bot = app.UseBotApplication(); // maps POST /api/messages

bot.OnActivity = async (activity, ct) =>
{
    if (activity.Type == ActivityType.Message)
    {
        var reply = CoreActivity.CreateBuilder()
            .WithType(ActivityType.Message)
            .WithConversation(activity.Conversation)
            .WithServiceUrl(activity.ServiceUrl)
            .WithProperty("text", "Hello from the bot!")
            .Build();

        await bot.SendActivityAsync(reply, ct);
    }
};

app.Run();

Custom Bot Subclass

public class MyBot : BotApplication
{
    public MyBot(
        ConversationClient conversationClient,
        UserTokenClient tokenClient,
        ILogger<MyBot> logger)
        : base(conversationClient, tokenClient, logger)
    {
        OnActivity = HandleActivityAsync;
    }

    private async Task HandleActivityAsync(CoreActivity activity, CancellationToken ct)
    {
        // your logic here
    }
}

// Registration
builder.AddBotApplication<MyBot>();
var bot = app.UseBotApplication<MyBot>();

Middleware

public class LoggingMiddleware : ITurnMiddleware
{
    public async Task OnTurnAsync(
        BotApplication bot, CoreActivity activity, NextTurn next, CancellationToken ct)
    {
        Console.WriteLine($"Activity: {activity.Type} from {activity.From?.Name}");
        await next(ct);
    }
}

bot.UseMiddleware(new LoggingMiddleware());

Extensible Activity Schema

public class MyChannelData : ChannelData
{
    [JsonPropertyName("customField")]
    public string? CustomField { get; set; }
}

public class MyActivity : CoreActivity
{
    [JsonPropertyName("channelData")]
    public new MyChannelData? ChannelData { get; set; }
}

Configuration

Provide credentials via appsettings.json:

{
  "AzureAd": {
    "Instance": "https://login.microsoftonline.com/",
    "TenantId": "<your-tenant-id>",
    "ClientId": "<your-client-id>",
    "Scope": "https://api.botframework.com/.default",
    "ClientCredentials": [
      {
        "SourceType": "ClientSecret",
        "ClientSecret": "<your-secret>"
      }
    ]
  }
}

Or via environment variables:

AzureAd__TenantId=<your-tenant-id>
AzureAd__ClientId=<your-client-id>
AzureAd__ClientCredentials__0__SourceType=ClientSecret
AzureAd__ClientCredentials__0__ClientSecret=<your-secret>

When no MSAL configuration is provided, communication happens as anonymous REST calls, suitable for localhost testing.

Design Principles

• Loose schema — CoreActivity contains only strictly required fields; additional fields are captured via JsonExtensionData
• Simple serialization — No custom converters; standard System.Text.Json with source generation
• Extensible schema — ChannelData and ConversationAccount support extension properties; generics allow custom types
• MSAL-based auth — Token acquisition built on top of Microsoft Identity Web
• ASP.NET DI — All dependencies configured via IServiceCollection extensions, reusing the existing HttpClient factory
• ILogger & IConfiguration — Standard .NET logging and configuration throughout

Main Types