Reference implementation of ApplicationOptionsPostConfigurer

ApplicationOptionsPostConfigurer.cs

using EPiServer.Cms.UI.AspNetIdentity;
using EPiServer.Data;
using Microsoft.Extensions.Options;
using System.Linq;

namespace YourProject.Infrastructure.Security
{
    public class ApplicationOptionsPostConfigurer : IPostConfigureOptions<ApplicationOptions>
    {
        private readonly IOptions<DataAccessOptions> _dataAccessOptions;

        public ApplicationOptionsPostConfigurer(IOptions<DataAccessOptions> dataAccessOptions)
        {
            _dataAccessOptions = dataAccessOptions;
        }

        public void PostConfigure(string name, ApplicationOptions options)
        {
            if (string.IsNullOrEmpty(options.ConnectionStringOptions?.ConnectionString))
            {
                options.ConnectionStringOptions = _dataAccessOptions.Value.ConnectionStrings.FirstOrDefault((ConnectionStringOptions c) => c.Name == _dataAccessOptions.Value.DefaultConnectionStringName);
            }
        }
    }
}