Sample code for https://stackoverflow.com/questions/52407867/how-to-initialize-a-dictionary-type-during-dependency-injection/52409026

appsettings.json

{
  "PhoneBookSection": {
    "John Doe": "555-123-456",
    "Jane Doe": "555-234-567"
  }
}

Program.cs

using System;
using System.Collections.Generic;
using Microsoft.Extensions.Configuration;

namespace Sample
{
    class Program
    {
        static readonly IConfiguration Configuration = new ConfigurationBuilder()
            .AddJsonFile("appsettings.json", optional: false, reloadOnChange: false)
            .Build();

        static void Main(string[] args)
        {
            const string PhoneBookSection = "PhoneBookSection";
            var phonebook = new Dictionary<string, string>();
            Configuration.Bind(PhoneBookSection, phonebook);

            foreach (var entry in phonebook)
                Console.WriteLine($"{entry.Key} - {entry.Value}");
        }
    }
}