一般情况下，ASP.NET Core应用程序使用cookie来存储用户身份验证信息。但是，如果您希望将主体数据存储在数据库中而不是cookie中，可以遵循以下步骤：

1. 创建一个标识服务器提供程序（Identity Server Provider）来支持存储用户的主体数据。可以从NuGet安装IdentityServer4包。

   Install-Package IdentityServer4
   

2. 创建一个自定义用户存储库（Custom User Store）来实现实际的数据库访问逻辑。该存储库应该实现AspNetCore.Identity.IUserStore接口和AspNetCore.Identity.IUserRoleStore接口。在此示例中，使用Entity Framework Core作为数据访问框架。该存储库可能如下所示：

   public class CustomUserStore : IUserStore, IUserRoleStore
   {
       private readonly ApplicationDbContext _dbContext;
    
       public CustomUserStore(ApplicationDbContext dbContext)
       {
           _dbContext = dbContext;
       }
    
       public async Task CreateAsync(ApplicationUser user, CancellationToken cancellationToken)
       {
           _dbContext.Users.Add(user);
           await _dbContext.SaveChangesAsync(cancellationToken);
    
           return IdentityResult.Success;
       }
    
       public async Task DeleteAsync(ApplicationUser user, CancellationToken cancellationToken)
       {
           _dbContext.Users.Remove(user);
           await _dbContext.SaveChangesAsync(cancellationToken);
       }
    
       public async Task FindByIdAsync(string userId, CancellationToken cancellationToken)
       {
           return await _dbContext.Users.FindAsync(new object[] { userId }, cancellationToken);
       }
    
       public async Task FindByNameAsync(string normalizedUserName, CancellationToken cancellationToken)
       {
           return await _dbContext.Users.FirstOrDefaultAsync(u => u.UserName == normalizedUserName, cancellationToken);
       }
    
       public Task GetNormalizedUserNameAsync(ApplicationUser user, CancellationToken cancellationToken)
       {
           return Task.FromResult(user.UserName);
       }
    
       public async Task GetUserIdAsync(ApplicationUser user, CancellationToken cancellationToken)
       {
           return (await _dbContext.Users.FirstOrDefaultAsync(u => u.Email == user