feat(backend): start authentication controllers

Foxnouns.Backend/Controllers/Authentication/AuthController.cs

@@ -0,0 +1,38 @@
+using System.Web;
+using Foxnouns.Backend.Services;
+using Microsoft.AspNetCore.Mvc;
+using NodaTime;
+
+namespace Foxnouns.Backend.Controllers.Authentication;
+
+[Route("/api/v2/auth")]
+public class AuthController(Config config, KeyCacheService keyCacheSvc) : ApiControllerBase
+{   
+    [HttpPost("urls")]
+    [ProducesResponseType(StatusCodes.Status200OK, Type = typeof(UrlsResponse))]
+    public async Task<IActionResult> UrlsAsync()
+    {
+        var state = HttpUtility.UrlEncode(await keyCacheSvc.GenerateAuthStateAsync());
+        string? discord = null;
+        if (config.DiscordAuth.ClientId != null && config.DiscordAuth.ClientSecret != null)
+            discord =
+                $"https://discord.com/oauth2/authorize?response_type=code" +
+                $"&client_id={config.DiscordAuth.ClientId}&scope=identify" +
+                $"&prompt=none&state={state}" +
+                $"&redirect_uri={HttpUtility.UrlEncode($"{config.BaseUrl}/auth/login/discord")}";
+
+        return Ok(new UrlsResponse(discord, null, null));
+    }
+
+    private record UrlsResponse(
+        string? Discord,
+        string? Google,
+        string? Tumblr
+    );
+
+    internal record AuthResponse(
+        UserRendererService.UserResponse User,
+        string Token,
+        Instant ExpiresAt
+    );
+}