Build Microsoft 365 Agents with .NET SDK

The skill covers building enterprise agents for Microsoft 365, Teams, and Copilot Studio on the Microsoft.Agents SDK, using ASP.NET Core hosting, agent routing, and MSAL-based authentication. Before implementation it tells the agent to use the microsoft-docs MCP to verify the latest AddAgent, AgentApplication, and authentication APIs, and to confirm NuGet package versions for the Microsoft.Agents.* packages in use.

It walks through the full setup: installing the required NuGet packages, configuring appsettings.json (TokenValidation with audience/tenant, AgentApplication typing/mention behavior, a ServiceConnection using ClientSecret auth against login.microsoftonline.com, and CopilotStudioClientSettings for direct-engine connections), and wiring an ASP.NET Core host that registers AddAgentApplicationOptions, AddAgent<MyAgent>, IStorage (MemoryStorage for development), AddAgentAspNetAuthentication, and a /api/messages POST route that hands the request to IAgentHttpAdapter.ProcessAsync, requiring authorization outside development. The routing layer is a subclass of AgentApplication that wires OnConversationUpdate (welcome new members), OnActivity for message handling, and OnTurnError to clear conversation state and send an end-of-conversation activity on failure.

For direct-to-engine Copilot Studio access it covers a DelegatingHandler that acquires an MSAL token silently for a cached account and falls back to an interactive AcquireTokenInteractive flow when silent acquisition fails, plus a console host that registers CopilotClient via IHttpClientFactory and streams activities through StartConversationAsync and AskQuestionAsync.

Install command, quoted verbatim from the source:

dotnet add package Microsoft.Agents.Hosting.AspNetCore
dotnet add package Microsoft.Agents.Authentication.Msal
dotnet add package Microsoft.Agents.Storage
dotnet add package Microsoft.Agents.CopilotStudio.Client
dotnet add package Microsoft.Identity.Client.Extensions.Msal

Six best practices close it out: centralize routing/error handling in AgentApplication subclasses, use MemoryStorage only in development and persisted storage in production, enable TokenValidation and require authorization on /api/messages in production, keep auth secrets in Key Vault/managed identity/environment variables rather than source, reuse HttpClient from IHttpClientFactory and cache MSAL tokens, and prefer async handlers with CancellationToken passed through SDK calls.

Use it when building a .NET agent that needs to run inside Microsoft 365, Teams, or Copilot Studio with ASP.NET Core hosting and MSAL authentication. It is not a substitute for environment-specific validation, testing, or expert review, and it stops for clarification when required inputs, permissions, safety boundaries, or success criteria are missing.

Input is the target agent's requirements (which channels, what auth model, whether Copilot Studio direct-engine access is needed). Output is a working ASP.NET Core or console host wired to the Microsoft.Agents SDK: package references, appsettings.json configuration, an AgentApplication subclass with message/error routing, and, where applicable, a token-acquisition handler and CopilotClient wiring.

It names a reference file, references/acceptance-criteria.md, for import paths, the hosting pipeline, Copilot Studio client patterns, and anti-patterns, plus six Microsoft Learn/GitHub reference links covering the Agents SDK overview, the AddAgent and AgentApplication APIs, MSAL authentication configuration options, Copilot Studio integration, and the official GitHub samples repository.

.NET developers building enterprise agents that need to run inside Microsoft 365, Teams, or Copilot Studio with production-grade authentication and hosting, rather than a bare bot-framework sample.