We will use the "appsettings.json" file to store the configurations and also read those configurations using JsonConfigurationProvider provided by Microsoft. 

Sample appsettings.json file:

"WebsiteSettings": {
    "Name": "Techieclues - A developer community website",
    "Header": {
      "MainBannerTitle": "Articles, Blogs and Q&As",
      "HomePageSize": 25,
      "RightSideMenu": true
    }
  }

WebsiteSettings.cs:

The class name and properties should match with the appsetting.json section.

public class WebsiteSettings
{
	public string Name { get; set; }
	public HeaderSettings Header { get; set; }
}
public class HeaderSettings
{        
	public string MainBannerTitle { get; set; }
	public int HomePageSize { get; set; }
	public bool RightSideMenu { get; set; }
}

Using Bind method of IConfiguration, we can easily get the values from the appsettings.json file.

var websiteSettings = new WebsiteSettings();
// Retrieving and binding WebsiteSettings section using IConfiguration.  
configuration.Bind("WebsiteSettings", websiteSettings);
// Serialize object
return Content(JsonConvert.SerializeObject(websiteSettings));

If you want to more details, please see our article, Getting Values From appsettings.json File In ASP.Net Core.