Dependency injection¶

This page covers registering an agent with the standard .NET host and its service container.

Register the agent¶

AddFadenAgent registers a FadenAgent as a singleton. The agent is built the first time it is requested, and the configuration callback gets the service provider, so tools, approval handlers and stores can come from the container.

using Faden.Agents;
using Faden.Auth;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;

var serverUrl = new Uri("https://ai.example.internal");

var builder = Host.CreateApplicationBuilder(args);
builder.Services.AddSingleton(new AgentTokenProvider(serverUrl, "my-assistant", new FileTokenStore()));
builder.Services.AddSingleton<PageTools>();
builder.Services.AddFadenAgent((agent, services) => agent
    .UseServer(serverUrl, services.GetRequiredService<AgentTokenProvider>())
    .UseAgent("my-assistant")
    .AddTools(services.GetRequiredService<PageTools>()));

using var host = builder.Build();

AddFadenAgent is in the Microsoft.Extensions.DependencyInjection namespace. It has two forms:

Form	Use it when
`AddFadenAgent((AgentBuilder agent, IServiceProvider services) => ...)`	The configuration needs services from the container.
`AddFadenAgent((AgentBuilder agent) => ...)`	It does not.

The registration uses TryAdd: if a FadenAgent is already registered, a second call adds nothing. The container disposes the agent when it is disposed.

Use the agent¶

Request FadenAgent like any other service:

public sealed class AssistantService(FadenAgent agent)
{
    public async Task<string> AskAsync(string question, CancellationToken cancellationToken)
    {
        var session = await agent.StartSessionAsync(cancellationToken: cancellationToken);
        var result = await session.SendAsync(question, cancellationToken);
        return result.Text;
    }
}

UseServer takes any ITokenProvider. Register the AgentTokenProvider as a singleton, as above, so the part of your application that signs the user in and the agent share it. The provider is created with the backend's URL (usually the server URL), the agent's slug and a token store.

An AgentTokenProvider created this way uses its own HttpClient for sign-in. If the server's certificate is issued by a CA the machine does not trust, pass an HttpClient that trusts it, for example one built on FadenTransport.CreateHandler(options) with TrustedCaCertificate set, and set the same certificate in UseServer's configure callback.

using Faden;
using Faden.Http;

var ca = File.ReadAllBytes("company-ca.crt");
var http = new HttpClient(FadenTransport.CreateHandler(new FadenClientOptions { TrustedCaCertificate = ca }));
var tokens = new AgentTokenProvider(serverUrl, "my-assistant", new FileTokenStore(), http);

builder.Services.AddSingleton(tokens);
builder.Services.AddFadenAgent((agent, services) => agent
    .UseServer(serverUrl, services.GetRequiredService<AgentTokenProvider>(),
        options => options.TrustedCaCertificate = ca)
    .UseAgent("my-assistant"));

For an application without a user at the keyboard, also register an approval handler that fits your case, or keep the default, which declines every call that needs approval.

Dependency injection¶

Register the agent¶

Use the agent¶

Sign-in in a hosted application¶