feat: JWT 토큰 기반 Admin 로그인 인증 완성

- AuthService로 JWT 토큰 생성 및 검증
- CustomAuthenticationStateProvider를 통한 Blazor 인증 통합
- LocalStorageService로 토큰 관리
- Login.razor 완전 재작성 (실제 DB 검증, 토큰 발급)
- BCrypt 기반 비밀번호 검증
- admin/admin123으로 테스트 가능

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

TaxBaik.Admin/Services/AuthService.cs

@@ -0,0 +1,96 @@
+using System.IdentityModel.Tokens.Jwt;
+using System.Security.Claims;
+using System.Text;
+using BCrypt.Net;
+using Microsoft.IdentityModel.Tokens;
+using TaxBaik.Domain.Entities;
+using TaxBaik.Domain.Interfaces;
+
+namespace TaxBaik.Admin.Services;
+
+public class AuthService
+{
+    private readonly IAdminUserRepository _adminUserRepository;
+    private readonly ILogger<AuthService> _logger;
+    private readonly string _jwtSecretKey;
+    private readonly int _tokenExpirationMinutes = 480; // 8시간
+
+    public AuthService(IAdminUserRepository adminUserRepository, ILogger<AuthService> logger, IConfiguration configuration)
+    {
+        _adminUserRepository = adminUserRepository;
+        _logger = logger;
+        _jwtSecretKey = configuration["Jwt:SecretKey"] ?? throw new InvalidOperationException("Missing 'Jwt:SecretKey' configuration.");
+    }
+
+    public async Task<string?> AuthenticateAndGenerateTokenAsync(string username, string password)
+    {
+        if (string.IsNullOrWhiteSpace(username) || string.IsNullOrWhiteSpace(password))
+        {
+            return null;
+        }
+
+        var user = await _adminUserRepository.GetByUsernameAsync(username);
+        if (user == null)
+        {
+            _logger.LogWarning("로그인 시도: 존재하지 않는 사용자 '{Username}'", username);
+            return null;
+        }
+
+        if (!BCrypt.Net.BCrypt.Verify(password, user.PasswordHash))
+        {
+            _logger.LogWarning("로그인 시도: 잘못된 비밀번호 '{Username}'", username);
+            return null;
+        }
+
+        _logger.LogInformation("로그인 성공: {Username}", username);
+        return GenerateJwtToken(user);
+    }
+
+    private string GenerateJwtToken(AdminUser user)
+    {
+        var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_jwtSecretKey));
+        var creds = new SigningCredentials(key, SecurityAlgorithms.HmacSha256);
+
+        var claims = new[]
+        {
+            new Claim(ClaimTypes.NameIdentifier, user.Id.ToString()),
+            new Claim(ClaimTypes.Name, user.Username),
+            new Claim("username", user.Username)
+        };
+
+        var token = new JwtSecurityToken(
+            issuer: "taxbaik-admin",
+            audience: "taxbaik-admin-client",
+            claims: claims,
+            expires: DateTime.UtcNow.AddMinutes(_tokenExpirationMinutes),
+            signingCredentials: creds);
+
+        return new JwtSecurityTokenHandler().WriteToken(token);
+    }
+
+    public ClaimsPrincipal? ValidateToken(string token)
+    {
+        try
+        {
+            var key = new SymmetricSecurityKey(Encoding.UTF8.GetBytes(_jwtSecretKey));
+            var handler = new JwtSecurityTokenHandler();
+            var principal = handler.ValidateToken(token, new TokenValidationParameters
+            {
+                ValidateIssuerSigningKey = true,
+                IssuerSigningKey = key,
+                ValidateIssuer = true,
+                ValidIssuer = "taxbaik-admin",
+                ValidateAudience = true,
+                ValidAudience = "taxbaik-admin-client",
+                ValidateLifetime = true,
+                ClockSkew = TimeSpan.Zero
+            }, out SecurityToken validatedToken);
+
+            return principal;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+}

TaxBaik.Admin/Services/CustomAuthenticationStateProvider.cs

@@ -0,0 +1,59 @@
+using System.Security.Claims;
+using Microsoft.AspNetCore.Components.Authorization;
+
+namespace TaxBaik.Admin.Services;
+
+public class CustomAuthenticationStateProvider : AuthenticationStateProvider
+{
+    private readonly ILocalStorageService _localStorage;
+    private readonly AuthService _authService;
+    private readonly ILogger<CustomAuthenticationStateProvider> _logger;
+
+    public CustomAuthenticationStateProvider(ILocalStorageService localStorage, AuthService authService, ILogger<CustomAuthenticationStateProvider> logger)
+    {
+        _localStorage = localStorage;
+        _authService = authService;
+        _logger = logger;
+    }
+
+    public override async Task<AuthenticationState> GetAuthenticationStateAsync()
+    {
+        try
+        {
+            var token = await _localStorage.GetItemAsStringAsync("auth_token");
+
+            if (string.IsNullOrEmpty(token))
+            {
+                return new AuthenticationState(new ClaimsPrincipal(new ClaimsIdentity()));
+            }
+
+            var principal = _authService.ValidateToken(token);
+            if (principal == null)
+            {
+                await _localStorage.RemoveItemAsync("auth_token");
+                return new AuthenticationState(new ClaimsPrincipal(new ClaimsIdentity()));
+            }
+
+            return new AuthenticationState(principal);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "인증 상태 조회 중 오류 발생");
+            return new AuthenticationState(new ClaimsPrincipal(new ClaimsIdentity()));
+        }
+    }
+
+    public async Task LoginAsync(string token)
+    {
+        await _localStorage.SetItemAsStringAsync("auth_token", token);
+
+        var principal = _authService.ValidateToken(token);
+        NotifyAuthenticationStateChanged(GetAuthenticationStateAsync());
+    }
+
+    public async Task LogoutAsync()
+    {
+        await _localStorage.RemoveItemAsync("auth_token");
+        NotifyAuthenticationStateChanged(GetAuthenticationStateAsync());
+    }
+}

TaxBaik.Admin/Services/ILocalStorageService.cs

@@ -0,0 +1,8 @@
+namespace TaxBaik.Admin.Services;
+
+public interface ILocalStorageService
+{
+    Task<string?> GetItemAsStringAsync(string key);
+    Task SetItemAsStringAsync(string key, string value);
+    Task RemoveItemAsync(string key);
+}

TaxBaik.Admin/Services/LocalStorageService.cs

@@ -0,0 +1,43 @@
+using Microsoft.JSInterop;
+
+namespace TaxBaik.Admin.Services;
+
+public class LocalStorageService : ILocalStorageService
+{
+    private readonly IJSRuntime _jsRuntime;
+
+    public LocalStorageService(IJSRuntime jsRuntime)
+    {
+        _jsRuntime = jsRuntime;
+    }
+
+    public async Task<string?> GetItemAsStringAsync(string key)
+    {
+        try
+        {
+            return await _jsRuntime.InvokeAsync<string>("localStorage.getItem", key);
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    public async Task SetItemAsStringAsync(string key, string value)
+    {
+        try
+        {
+            await _jsRuntime.InvokeVoidAsync("localStorage.setItem", key, value);
+        }
+        catch { }
+    }
+
+    public async Task RemoveItemAsync(string key)
+    {
+        try
+        {
+            await _jsRuntime.InvokeVoidAsync("localStorage.removeItem", key);
+        }
+        catch { }
+    }
+}