Set a class private string parameter with some value at build time in .net core 3.1 class library project

I have a class in my .net core 3.1 library project where i want to initialize a key at compile time

```
using System.Text;

namespace MyNamespace
{
public class Myclass
{
private string key;

....
}
}
```

I am publishing my library via simple publish command

`dotnet publish -c release -r linux-x64 `
I am exploring an option where i could pass some attribute during compilation which will be set in key property after compilation. I am also obfuscating my dll as well after inital compilation via some third party tool