Blog: Custom Configuration Providers in ASP.NET Core

configuration-provider.cs

public class SqlServerConfigurationProvider : ConfigurationProvider , IDisposable
{
    private readonly SqlServerConfigurationSource _configurationSource;

    public SqlServerConfigurationProvider(SqlServerConfigurationSource configurationSource)
    {
        _configurationSource = configurationSource;
    }

    public override void Load()
    {
        // here you should connect to sql server and fetch the configurations
    }

    public void Dispose()
    {
        // cleanup all the resources
    }
}

configuration-source.cs

public class SqlServerConfigurationSource : IConfigurationSource
{
    public string Server { get; set; } = "localhost";
    public string Database { get; set; } = "ConfigurationDb";
    public string User { get; set; } = "sa";
    public string Password { get; set; } = "yourStrong(!)Password";
    public string Table { get; set; } = "dbo.Configuration";
    public string KeyColumn { get; set; } = "Key";
    public string ValueColumn { get; set; } = "Value";

    public IConfigurationProvider Build(IConfigurationBuilder builder)
            => new SqlServerConfigurationProvider(this);
}

create-schema.sql

CREATE  TABLE dbo.Configuration(

        [Key]   NVarChar(50)    NOT NULL PRIMARY KEY
    ,   [Value] NVarCHar(50)    NOT NULL
)
GO

program.cs

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureAppConfiguration(configure =>
        {
            configure.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true);
            configure.AddSqlServerDb();
        })
        .ConfigureWebHostDefaults(webBuilder => { webBuilder.UseStartup<Startup>(); });