Feat: 添加、优化账户相关功能

Authentication/MicrosoftAuthentication.cs

@@ -55,7 +55,7 @@
         var resultDict = new RetrieveDeviceCode
         {
             ClientId = ClientId,
             UserCode = responseDict.UserCode,
             DeviceCode = responseDict.DeviceCode,
             VerificationUri = responseDict.VerificationUri,
             Message = responseDict.Message
@@ -95,7 +95,7 @@
             if (tokenRes.IsSuccessStatusCode)
             {
                 var tokenData = tokenJson.ToJsonEntry<GetTokenResponse>();
                 if (!string.IsNullOrEmpty(tokenData.AccessToken))
                     return new GetTokenResponse
                     {
                         ExpiresIn = tokenData.ExpiresIn,
@@ -104,6 +104,31 @@
                         ClientId = deviceCodeInfo.ClientId
                     };
             }
+            else
+            {
+                // 先判断是否正在等待中，直接使用 Contains，避免额外解析开销
+                if (!tokenJson.Contains("authorization_pending"))
+                {
+                    try
+                    {
+                        var errorData = tokenJson.ToJsonEntry<GetTokenErrorResponse>();
+                        switch (errorData.Error)
+                        {
+                            case "authorization_declined":
+                                throw new Exception("用户拒绝了授权");
+                            case "bad_verification_code":
+                                throw new Exception("提交的 device_code 无效");
+                            case "expired_token":
+                                throw new TimeoutException("登录已超时,请重试"); // 避免轮询时正好过期导致抓不到异常
+                            // 实际上还有其他的错误类型，但按理说不会出现，比如 slow_down
+                        }
+                    }
+                    catch (Exception e)
+                    {
+                        throw new Exception("轮询获取 Token 错误：" + e.Message);
+                    }
+                }
+            }
 
             await Task.Delay(pollingInterval);
         }

Models/Authentication/GetTokenErrorResponse.cs

@@ -0,0 +1,15 @@
+using System.Text.Json.Serialization;
+
+namespace StarLight_Core.Models.Authentication;
+
+/// <summary>
+/// 令牌错误信息
+/// </summary>
+public class GetTokenErrorResponse
+{
+    /// <summary>
+    /// 验证令牌
+    /// </summary>
+    [JsonPropertyName("error")]
+    public string Error { get; set; }
+}

Skin/Fetchers/YggdrasilSkinFetcher.cs

@@ -0,0 +1,44 @@
+using StarLight_Core.Models.Authentication;
+using StarLight_Core.Models.Skin;
+using StarLight_Core.Utilities;
+using System.Security.Cryptography.X509Certificates;
+using System.Security.Principal;
+using System.Text;
+
+namespace StarLight_Core.Skin.Fetchers;
+
+/// <summary>
+/// 外置皮肤获取器
+/// </summary>
+public class YggdrasilSkinFetcher
+{
+    /// <summary>
+    /// 获取外置皮肤
+    /// </summary>
+    /// <param name="account">外置账户</param>
+    /// <returns>皮肤图片字节信息</returns>
+    public static async Task<byte[]> GetYggdrasilSkinAsync(YggdrasilAccount account)
+    {
+        return await GetYggdrasilSkinAsync(account.ServerUrl, account.Uuid);
+    }
+
+    /// <summary>
+    /// 获取外置皮肤
+    /// </summary>
+    /// <param name="serverUrl">服务器 Url</param>
+    /// <param name="uuid">外置账户 Uuid</param>
+    /// <returns></returns>
+    public static async Task<byte[]> GetYggdrasilSkinAsync(string serverUrl, string uuid)
+    {
+        var baseUrl = serverUrl.TrimEnd("/");
+        var skinJson = await HttpUtil.GetStringAsync($"{baseUrl}/sessionserver/session/minecraft/profile/{uuid}");
+        var skinUrl =
+            Encoding.UTF8.GetString(
+                    Convert.FromBase64String(
+                        skinJson.ToJsonEntry<ProfileJsonEntity>().Properties.First().Value))
+                .ToJsonEntry<SkinJsonEntity>()
+                .Textures.Skin.Url;
+        using var httpClient = new HttpClient();
+        return await httpClient.GetByteArrayAsync(skinUrl);
+    }
+}