重构项目结构，移除Assignment相关功能，优化Submission模块

TechHelper.Server/Services/User/IAuthenticationService.cs

@@ -0,0 +1,14 @@
+using TechHelper.Context;
+using Microsoft.AspNetCore.Identity;
+using System.Security.Claims;
+using Entities.Contracts;
+
+namespace TechHelper.Services.Beta
+{
+	public interface IAuthenticationService
+	{
+		public Task<string> GetToken(Entities.Contracts.User user);
+		public string GenerateRefreshToken();
+		public ClaimsPrincipal GetPrincipalFromExpiredToken(string token);	
+	}
+}