## Update for .NET Core 3.0+

1. You can use [`CreateDefaultBuilder`][1] which will automatically build and pass a configuration object to your startup class:

 ```cs
 WebHost.CreateDefaultBuilder(args).UseStartup<Startup>();
 ```
 
 ```cs
 public class Startup
 {
 public Startup(IConfiguration configuration) // automatically injected
 {
 Configuration = configuration;
 }
 public IConfiguration Configuration { get; }
 /* ... */
 }
 ```

2. `CreateDefaultBuilder` automatically includes the appropriate <code>appsettings.Environment.json</code> file so add a separate appsettings file for each environment:

 [![appsettings.env.json][2]][2]

3. Then set the `ASPNETCORE_ENVIRONMENT` **environment variable** when running / debugging

## How to set Environment Variables

Depending on your IDE, there are a couple places dotnet projects traditionally look for environment variables:

* For **Visual Studio** go to Project > Properties > Debug > Environment Variables:

 [![Visual Studio - Environment Variables][3]][3]


* For **Visual Studio Code**, edit `.vscode/launch.json` > `env`:

 [![Visual Studio Code > Launch Environment][4]][4]


* Using **Launch Settings**, edit `Properties/launchSettings.json` > `environmentVariables`:

 [![Launch Settings][6]][6]

 Which can also be selected from the Toolbar in Visual Studio

 [![Launch Settings Dropdown][7]][7]


* Using **dotnet CLI**, use the appropriate syntax for [setting environment variables per your OS][16]

 > **Note**: When an app is launched with [dotnet run][5], `launchSettings.json` is read if available, and `environmentVariables` settings in launchSettings.json override environment variables.

### How does `Host.CreateDefaultBuilder` work?

.NET Core 3.0 added [`Host.CreateDefaultBuilder`][1] under platform extensions which will provide a default initialization of [`IConfiguration`][8] which provides default configuration for the app in the following order:


> 1. `appsettings.json` using the [JSON configuration provider][9].
> 2. <code>appsettings.Environment.json</code> using the [JSON configuration provider][9]. For example:
> * <code>appsettings.Production.json</code> or
> * <code>appsettings.Development.json</code>
> 4. [App secrets][10] when the app runs in the Development environment.
> 5. Environment variables using the [Environment Variables configuration provider][11].
> 6. Command-line arguments using the [Command-line configuration provider][12].


### Further Reading - MS Docs

* [App startup in ASP.NET Core][13]
* [Configuration in ASP.NET Core][14]
* [Use multiple environments in ASP.NET Core][15]


 [1]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.hosting.host.createdefaultbuilder
 [2]: https://i.stack.imgur.com/qXihz.png
 [3]: https://i.stack.imgur.com/WSNlA.png
 [4]: https://i.stack.imgur.com/Qy8f5.png
 [5]: https://learn.microsoft.com/en-us/dotnet/core/tools/dotnet-run
 [6]: https://i.stack.imgur.com/JOGFp.png
 [7]: https://i.stack.imgur.com/dVEeO.png
 [8]: https://learn.microsoft.com/en-us/dotnet/api/microsoft.extensions.configuration.iconfiguration
 [9]: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration/#file-configuration-provider
 [10]: https://learn.microsoft.com/en-us/aspnet/core/security/app-secrets
 [11]: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration/#evcp
 [12]: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration/#command-line
 [13]: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/startup
 [14]: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/configuration
 [15]: https://learn.microsoft.com/en-us/aspnet/core/fundamentals/environments
 [16]: https://stackoverflow.com/a/43992754/1366033

I've defined some values in my `appsettings.json` for things like database connection strings, webapi locations and the like which are different for development, staging and live environments.

Is there a way to have multiple `appsettings.json` files (like `appsettings.live.json`, etc, etc) and have the asp.net app just 'know' which one to use based on the build configuration it's running?

Automatically set appsettings.json for dev and release environments in asp.net core?

You need to use two hyphens. The flag is `-t` or `--trust`, not `–trust` so the following should work:


```bash
dotnet dev-certs https --trust
```

You can also run the help command to see more info

```bash
dotnet dev-certs https --help
```

[![dev-certs https help output][1]][1]



**See Also**: [How to run `dotnet dev-certs https --trust`?][2]



[1]: https://i.stack.imgur.com/zlr6u.png
[2]: https://stackoverflow.com/q/55485511/1366033

I have a problem with HTTPS when I am running (`dotnet run`) my .NetCore application locally on Windows.
It was working till my localhost certificate expired…

[![][1]][1]

I clean up old certificates and generated the new one by 

    dotnet dev-certs https –clean
    dotnet dev-certs https –trust

I’ve verified that everything was added to certmgr (Personal and Trusted certs), but I have the same problem.
It is keep trying to use old certificate which expired.
I do not know why it is trying to use old “localhost” certificate after clean up certs…

Do you have any idea what should I do?.

Thank you,
Błażej


  [1]: https://i.stack.imgur.com/A6cN6.jpg