Добавьте файлы проекта.

PlaylistShared.Api/Extensions/ClaimsPrincipalExtensions.cs

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+using System.Security.Claims;
+
+namespace PlaylistShared.Api.Extensions;
+
+public static class ClaimsPrincipalExtensions
+{
+    public static Guid GetUserId(this ClaimsPrincipal user)
+    {
+        var id = user.FindFirst(ClaimTypes.NameIdentifier)?.Value;
+        if (string.IsNullOrEmpty(id))
+            throw new UnauthorizedAccessException("User ID not found");
+        return Guid.Parse(id);
+    }
+
+    public static Guid? GetUserIdOrNull(this ClaimsPrincipal user)
+    {
+        var id = user.FindFirst(ClaimTypes.NameIdentifier)?.Value;
+        return string.IsNullOrEmpty(id) ? null : Guid.Parse(id);
+    }
+}

PlaylistShared.Api/Extensions/YCoverExtensions.cs

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+using YandexMusic.API.Models.Common.Cover;
+
+namespace PlaylistShared.Api.Extensions;
+
+public static class YCoverExtensions
+{
+    public static string GetUrl(this YCover cover, string size = "200x200")
+    {
+        switch (cover)
+        {
+            case YCoverImage img when !string.IsNullOrEmpty(img.Uri):
+                return $"https://{img.Uri.Replace("%%", size)}";
+            case YCoverPic pic when !string.IsNullOrEmpty(pic.Uri):
+                return $"https://{pic.Uri.Replace("%%", size)}";
+            default:
+                return string.Empty;
+        }
+    }
+}