Is it possible to reconfigure App configuration after "CreateDefaultBuilder" call

Question

In CreateDefaultBuilder a call is made to ConfigureAppConfiguration with some defaults. I'd like to override (or append) to these defaults. I've tried copying CreateDefaultBuilder into my own function and editing the appropriate lines, however it can't resolve a type used in the function because the type is internal to AspNetCore namespaces (specifically the HostFilteringStartupFilter type).

Is there some cleaner way for me to modify the CreateDefaultBuilder functionality?

EDIT: So I just looked at the source of HostFilteringStartupFilter and it just calls UseHostFiltering on the IApplicationBuilder, so I just added that to my Startup.Configure but I would still like a cleaner approach if possible..

Answer 1

CreateDefaultBuilder sets up reasonable defaults that you want to preserve except the configuration part. CreateDefaultBuilder performs the following configuration setup:

1. appsettings.json
2. appsettings.{Environment}.json
3. Secret Manager (if Development environment)
4. Environment variables.
5. Command-line arguments.

Knowing this default layering, the fact that every layer can potentially override values in previous ones and the fact that you can only add configuration providers to the list (while not being able to remove them), you can now solve your problem.

Overriding configuration on top of CreateDefaultBuilder is done using ConfigureAppConfiguration :

    WebHost.CreateDefaultBuilder(args)
        .ConfigureAppConfiguration((hostingContext, config) =>
        {
            // Override here specifying new or previous layers to make sure 
            // you get the desired outcome.
            // e.g. If you specify your appsettings.json you basically start from scratch
            ...

        })...