taxbaik/TaxBaik.Web/Services/TokenRefreshHandler.cs

namespace TaxBaik.Web.Services;

using System.Net;
using System.Text.Json;

/// <summary>
/// HTTP 요청 시 자동으로 access token을 추가하고,
/// 401 응답을 받으면 refresh token으로 새 토큰을 획득한 후 재시도합니다.
/// SOLID: Single Responsibility - 토큰 갱신 로직만 담당
/// </summary>
public class TokenRefreshHandler : DelegatingHandler
{
    private readonly ILocalStorageService _localStorage;
    private readonly ILogger<TokenRefreshHandler> _logger;

    public TokenRefreshHandler(ILocalStorageService localStorage, ILogger<TokenRefreshHandler> logger)
    {
        _localStorage = localStorage;
        _logger = logger;
    }

    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request,
        CancellationToken cancellationToken)
    {
        // 요청에 access token 추가
        var accessToken = await _localStorage.GetItemAsStringAsync("accessToken");
        if (!string.IsNullOrEmpty(accessToken))
        {
            request.Headers.Authorization = new("Bearer", accessToken);
        }

        var response = await base.SendAsync(request, cancellationToken);

        // 401 응답이면 토큰 갱신 시도
        if (response.StatusCode == HttpStatusCode.Unauthorized)
        {
            var refreshToken = await _localStorage.GetItemAsStringAsync("refreshToken");
            if (!string.IsNullOrEmpty(refreshToken))
            {
                var newTokenPair = await RefreshTokenAsync(refreshToken, request, cancellationToken);
                if (newTokenPair != null)
                {
                    // 토큰 저장
                    await _localStorage.SetItemAsStringAsync("accessToken", newTokenPair.AccessToken);
                    await _localStorage.SetItemAsStringAsync("refreshToken", newTokenPair.RefreshToken);
                    await _localStorage.SetItemAsStringAsync("tokenExpiry",
                        DateTime.UtcNow.AddSeconds(newTokenPair.ExpiresIn).Ticks.ToString());

                    // 새 토큰으로 재요청
                    request.Headers.Authorization = new("Bearer", newTokenPair.AccessToken);
                    response = await base.SendAsync(request, cancellationToken);
                }
                else
                {
                    _logger.LogWarning("토큰 갱신 실패 - 로그아웃");
                    await _localStorage.RemoveItemAsync("accessToken");
                    await _localStorage.RemoveItemAsync("refreshToken");
                    await _localStorage.RemoveItemAsync("tokenExpiry");
                }
            }
        }

        return response;
    }

    private async Task<AuthTokenPair?> RefreshTokenAsync(string refreshToken, HttpRequestMessage originalRequest, CancellationToken ct)
    {
        try
        {
            // 원래 요청의 호스트 정보 추출
            var authority = originalRequest.RequestUri?.Authority ?? "localhost:5001";
            var scheme = originalRequest.RequestUri?.Scheme ?? "http";

            using var httpClient = new HttpClient();
            var refreshUri = new Uri($"{scheme}://{authority}/taxbaik/api/auth/refresh");
            var json = JsonSerializer.Serialize(new { refreshToken });
            var content = new StringContent(json, System.Text.Encoding.UTF8, "application/json");

            var response = await httpClient.PostAsync(refreshUri, content, ct);
            if (!response.IsSuccessStatusCode)
            {
                _logger.LogWarning($"Token refresh failed with status {response.StatusCode}");
                return null;
            }

            var responseContent = await response.Content.ReadAsStringAsync(ct);
            var result = JsonSerializer.Deserialize<AuthTokenResponse>(responseContent,
                new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

            return result != null
                ? new AuthTokenPair(result.AccessToken, result.RefreshToken, result.ExpiresIn)
                : null;
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Exception during token refresh");
            return null;
        }
    }
}

internal class AuthTokenResponse
{
    public string AccessToken { get; set; } = string.Empty;
    public string RefreshToken { get; set; } = string.Empty;
    public int ExpiresIn { get; set; }
}