Foxnouns.NET/Foxnouns.Backend/Controllers/Authentication/FediverseAuthController.cs

using Foxnouns.Backend.Database;
using Foxnouns.Backend.Database.Models;
using Foxnouns.Backend.Services;
using Foxnouns.Backend.Services.Auth;
using Foxnouns.Backend.Utils;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using NodaTime;

namespace Foxnouns.Backend.Controllers.Authentication;

[Route("/api/internal/auth/fediverse")]
public class FediverseAuthController(
    ILogger logger,
    DatabaseContext db,
    FediverseAuthService fediverseAuthService,
    AuthService authService,
    KeyCacheService keyCacheService
) : ApiControllerBase
{
    private readonly ILogger _logger = logger.ForContext<FediverseAuthController>();

    [HttpGet]
    [ProducesResponseType<FediverseUrlResponse>(statusCode: StatusCodes.Status200OK)]
    public async Task<IActionResult> GetFediverseUrlAsync([FromQuery] string instance)
    {
        if (instance.Any(c => c is '@' or ':' or '/') || !instance.Contains('.'))
            throw new ApiError.BadRequest("Not a valid domain.", "instance", instance);

        var url = await fediverseAuthService.GenerateAuthUrlAsync(instance);
        return Ok(new FediverseUrlResponse(url));
    }

    [HttpPost("callback")]
    [ProducesResponseType<CallbackResponse>(statusCode: StatusCodes.Status200OK)]
    public async Task<IActionResult> FediverseCallbackAsync([FromBody] CallbackRequest req)
    {
        var app = await fediverseAuthService.GetApplicationAsync(req.Instance);
        var remoteUser = await fediverseAuthService.GetRemoteFediverseUserAsync(app, req.Code);

        var user = await authService.AuthenticateUserAsync(
            AuthType.Fediverse,
            remoteUser.Id,
            instance: app
        );
        if (user != null)
            return Ok(await authService.GenerateUserTokenAsync(user));

        var ticket = AuthUtils.RandomToken();
        await keyCacheService.SetKeyAsync(
            $"fediverse:{ticket}",
            new FediverseTicketData(app.Id, remoteUser),
            Duration.FromMinutes(20)
        );

        return Ok(
            new CallbackResponse(
                HasAccount: false,
                Ticket: ticket,
                RemoteUsername: $"@{remoteUser.Username}@{app.Domain}",
                User: null,
                Token: null,
                ExpiresAt: null
            )
        );
    }

    [HttpPost("register")]
    [ProducesResponseType<AuthController.AuthResponse>(statusCode: StatusCodes.Status200OK)]
    public async Task<IActionResult> RegisterAsync(
        [FromBody] AuthController.OauthRegisterRequest req
    )
    {
        var ticketData = await keyCacheService.GetKeyAsync<FediverseTicketData>(
            $"fediverse:{req.Ticket}"
        );
        if (ticketData == null)
            throw new ApiError.BadRequest("Invalid ticket", "ticket", req.Ticket);

        var app = await db.FediverseApplications.FindAsync(ticketData.ApplicationId);
        if (
            await db.AuthMethods.AnyAsync(a =>
                a.AuthType == AuthType.Fediverse
                && a.RemoteId == ticketData.User.Id
                && a.FediverseApplicationId == app.Id
            )
        )
        {
            _logger.Error(
                "Fediverse user {Id}/{ApplicationId} ({Username} on {Domain}) has valid ticket but is already linked to an existing account",
                ticketData.User.Id,
                ticketData.ApplicationId,
                ticketData.User.Username,
                app.Domain
            );
            throw new ApiError.BadRequest("Invalid ticket", "ticket", req.Ticket);
        }

        var user = await authService.CreateUserWithRemoteAuthAsync(
            req.Username,
            AuthType.Fediverse,
            ticketData.User.Id,
            ticketData.User.Username,
            instance: app
        );

        return Ok(await authService.GenerateUserTokenAsync(user));
    }

    public record CallbackRequest(string Instance, string Code);

    private record FediverseUrlResponse(string Url);

    private record FediverseTicketData(
        Snowflake ApplicationId,
        FediverseAuthService.FediverseUser User
    );
}