How do I add custom application settings?

There are many ways to supply custom application settings e.g. connection strings to your application, and the official ASP .NET documentation explains in great detail the various options you have available.

Configuration of the Server

In this recipe, we show how to add configuration using an appsettings.json configuration file.

Never store secrets in plain text files such as appsettings.json - our recommendation is to use it for non-secret configuration data that is shared across your development team; see here for more guidance.

1. In the Server folder, add a file appsettings.json. It does not need to be added to the project file.
2. Add the following content to it:

   {
       "MyKey": "My appsettings.json Value"
   }
   

3. In Server.fs, ensure that your API builder functions take in an HTTPContext as an argument and change the construction of your Fable Remoting endpoint to supply one:

   ++open Microsoft.AspNetCore.Http
   
   --let todosApi = {
   ++let todosApi (context: HttpContext) = {
   
   ...
   
   --    |> Remoting.fromValue todosApi
   ++    |> Remoting.fromContext todosApi
   

4. Use the context to get a handle to the IConfiguration object, which allows you to access settings regardless of what infrastructure you are using to store them e.g. appsettings.json, environment variables etc.

   ++open Giraffe
   ++open Microsoft.Extensions.Configuration
   
   let todosApi (context: HttpContext) =
   ++    let cfg = context.GetService<IConfiguration>()
   ++    let value = cfg["MyKey"] // "My appsettings.json Value"
   

   Note that the todosApi function will be called on every single ASP .NET request. It is safe to "capture" the cfg value and use it across multiple API methods.

Publishing settings files

Be aware that appsettings.json files will be included in your bundle by default. However, depending on your application, it can be overridden by e.g. environment variables.

Working with User Secrets

User Secrets are an alternative way of storing secrets which, although still stored in plain text files, are not stored in your repository folder and therefore less at risk to accidentally committing into source control. However, Saturn currently disables User Secrets as part of its startup routine, and you must manually turn them back on:

++type DummyType() = class end

let app = application {
++    host_config (fun hostBuilder ->
++        hostBuilder.ConfigureAppConfiguration(fun _ configBuilder ->
++            configBuilder.AddUserSecrets<DummyType>()
++            |> ignore
++        )
++    )
}

You can then access the IConfiguration as before, and user secrets values will be accessible.

Configuration of the client

Configuration of the client can be done in many ways, but generally a simple strategy is to have an API endpoint which is called on startup that provides any settings required by the client.