public class DatabaseConfigurationSource : IConfigurationSource
   {
       private readonly string _connectionString;
       
       public DatabaseConfigurationSource(string connectionString)
       {
           _connectionString = connectionString;
       }
       
       public IConfigurationProvider Build(IConfigurationBuilder builder)
       {
           return new DatabaseConfigurationProvider(
               new SqlConnection(_connectionString)
           );
       }
   }