appsettings.json

In previous versions of ASP.NET, we store application configuration settings, like, for example, database connection strings in web.config file.

In ASP.NET Core application configuration settings can come from the following different configurations sources:

Files: (appsettings.json, appsettings.{Environment}.json, where {Environment} is the api's current hosting environment)
User secrets
Environment variables
Command-line arguments

The latest configuration source overwrite previous configuration source. If same Key exists in both appsettings.json and as an Envionment Varaible, the Environment Variable orerwrites the one in appsettings.json file

The appsettings.json, (or appsettings.development.json) were created during the project cteation.

In this file we can set new configurations for our application, It is set in a key, value pairs in a JSON format. Let's add, for example, new key named MyKey:
```
{
"Logging": {
    "LogLevel": {
    "Default": "Information",
    "Microsoft.AspNetCore": "Warning"
    }
},
"AllowedHosts": "*",

"MyKey": "Value of MyKey from appsettings.json"
}
```
- To access configuration information, we need access to IConfiguration service provided by the framework. We can get it in several ways two of them are:
- Read configuration directly from the builder (the simplest way)
```
_config = builder.Configuration;
```
  while keeping the _config variable as a private memeber in the class
- Let DI inject I_Configuration into a minimal API handler
```
app.MapGet("/", (IConfiguration config) => {
    string? configValue = config["MyKey"];
    return configValue;
});
```
  - Note: If you want to use IConfiguration in a non-minimal API handler, we can also register it as a service: builder.Services.AddSingleton<IConfiguration>(builder.Configuration); Then we can inject IConfiguration into any class constructor
  - In this case Since IConfiguration is registered as a service by default, we can directly inject it into the minimal API handler without needing to register it explicitly
  - IConfiguration service is registered as a singletone, so in any request we will get the same instance, (so we don't need to keep it in this class)
  - Note: If you want to read configuration in a non-minimal API handler, you can also use the static property ConfigurationManager.AppSettings["MyKey"] to read configuration values without needing to inject IConfiguration