feat(backend): add RequestDiscordTokenAsync method

Foxnouns.Backend/Controllers/Authentication/DiscordAuthController.cs

@@ -1,16 +1,61 @@
 using Foxnouns.Backend.Database;
+using Foxnouns.Backend.Database.Models;
+using Foxnouns.Backend.Services;
 using Microsoft.AspNetCore.Mvc;
+using NodaTime;
 
 namespace Foxnouns.Backend.Controllers.Authentication;
 
 [Route("/api/v2/auth/discord")]
-public class DiscordAuthController(Config config, DatabaseContext db) : ApiControllerBase
+public class DiscordAuthController(
+    Config config,
+    ILogger logger,
+    IClock clock,
+    DatabaseContext db,
+    KeyCacheService keyCacheSvc,
+    AuthService authSvc,
+    RemoteAuthService remoteAuthSvc,
+    UserRendererService userRendererSvc) : ApiControllerBase
 {
+    [HttpPost("callback")]
+    public async Task<IActionResult> CallbackAsync([FromBody] AuthController.CallbackRequest req)
+    {
+        CheckRequirements();
+        await keyCacheSvc.ValidateAuthStateAsync(req.State);
+
+        var remoteUser = await remoteAuthSvc.RequestDiscordTokenAsync(req.Code, req.State);
+        var user = await authSvc.AuthenticateUserAsync(AuthType.Discord, remoteUser.Id);
+        if (user != null) return Ok(await GenerateUserTokenAsync(user));
+
+        logger.Debug("Discord user {Username} ({Id}) authenticated with no local account", remoteUser.Username,
+            remoteUser.Id);
+
+        throw new NotImplementedException();
+    }
+
+    private async Task<AuthController.AuthResponse> GenerateUserTokenAsync(User user)
+    {
+        var frontendApp = await db.GetFrontendApplicationAsync();
+        logger.Debug("Logging user {Id} in with Discord", user.Id);
+
+        var (tokenStr, token) =
+            authSvc.GenerateToken(user, frontendApp, ["*"], clock.GetCurrentInstant() + Duration.FromDays(365));
+        db.Add(token);
+
+        logger.Debug("Generated token {TokenId} for {UserId}", user.Id, token.Id);
+
+        await db.SaveChangesAsync();
+
+        return new AuthController.AuthResponse(
+            await userRendererSvc.RenderUserAsync(user, selfUser: user, renderMembers: false),
+            tokenStr,
+            token.ExpiresAt
+        );
+    }
+
     private void CheckRequirements()
     {
-        if (config.DiscordAuth.ClientId == null || config.DiscordAuth.ClientSecret == null)
-        {
+        if (!config.DiscordAuth.Enabled)
             throw new ApiError.BadRequest("Discord authentication is not enabled on this instance.");
-        }
     }
 }