C# - how to get the name of internal variables used in a method

How is it possible (maybe through Reflection or Roslyn APIs) to get the list of internal variables that are used in a class method?

For example, in the following code:

class C1{
   private int var1;
   public string var2;

   void action1()
    {
       int var3;
       var3=var1*var1;
       var2="Completed";
   }
}

I would like to get var3,var1 and var2 as the list(as name and type) of variables used in the action1() method.

Secondly, I need to identify which of the above variables appear on the left side of an expression; i.e., their values have been modified in this method.

I think the answer lies in using Roslyn, but I have no idea how. Thanks!