public static class DbOptionsFactory
{
    static DbOptionsFactory()
    {
        var config = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json")
            .Build();
        var connectionString = config["Data:DefaultConnection:ConnectionString"];

        DbContextOptions = new DbContextOptionsBuilder<MyDbContext>()
            .UseSqlServer(connectionString)
            .Options;
    }

    public static DbContextOptions<MyDbContext> DbContextOptions { get; }

}

{
  "Data": {
  "DefaultConnection": {
      "Name": "MyDbContext",
      "ConnectionString": "connection string goes here"
   }
 }
}

using (var context = new JmsDbContext(DbOptionsFactory.DbContextOptions))
{
     // access db here
}