chat: add hello controller

Foxchat.Chat/Controllers/HelloController.cs

@@ -0,0 +1,45 @@
+using Foxchat.Chat.Database;
+using Foxchat.Chat.Database.Models;
+using Foxchat.Chat.Middleware;
+using Foxchat.Core.Extensions;
+using Foxchat.Core.Federation;
+using Foxchat.Core.Models.Http;
+using Microsoft.AspNetCore.Mvc;
+using ApiError = Foxchat.Core.ApiError;
+
+namespace Foxchat.Chat.Controllers;
+
+[ApiController]
+[Unauthenticated]
+[Route("/_fox/chat/hello")]
+public class HelloController(
+    ILogger logger,
+    ChatContext db,
+    InstanceConfig config,
+    RequestSigningService requestSigningService)
+    : ControllerBase
+{
+    [HttpPost]
+    public async Task<IActionResult> Hello([FromBody] Hello.HelloRequest req)
+    {
+        var node = await requestSigningService.RequestAsync<Hello.NodeInfo>(HttpMethod.Get, req.Host,
+            "/_fox/ident/node");
+
+        if (!HttpContext.ExtractRequestData(out var signature, out var domain, out var signatureData))
+            throw new ApiError.IncomingFederationError("This endpoint requires signed requests.");
+
+        if (!requestSigningService.VerifySignature(node.PublicKey, signature, signatureData))
+            throw new ApiError.IncomingFederationError("Signature is not valid.");
+
+        var instance = await db.GetInstanceAsync();
+        db.IdentityInstances.Add(new IdentityInstance
+        {
+            Domain = req.Host,
+            BaseUrl = $"https://{req.Host}",
+            PublicKey = node.PublicKey
+        });
+        await db.SaveChangesAsync();
+
+        return Ok(new Hello.HelloResponse(instance.PublicKey, config.Domain));
+    }
+}