App secrets in dot net core

Create new application in dotnet core using CLI or Visual Studio IDE
Go to project directory and run below command

dotnet user-secrets initdotnet user-secrets set "Key_name" "key_value"

now get value using
Environment.GetEnvironmentVariable("Key_name");
or
private readonly IConfiguration _config;
public Classtest(IConfiguration config)
{
_config = config;
}

string _key=_config["Key_name"]