Scala: How to access associated parameter values of a macro annotation in the macro implementation?

Question

I am working with macro annotations (link) that are part of the macro paradise of Scala.

In their example they use a macro annotation called identity which takes no parameters. However, the macro annotation I am trying to implement does require an argument:

@compileTimeOnly("enable macro paradise to expand macro annotations")
class f(id: String) extends StaticAnnotation {
  def macroTransform(annottees: Any*) = macro identityMacro.impl
}

object identityMacro extends App {
  def impl(c: Context)(annottees: c.Expr[Any]*) = {
    import c.universe._
    // how to access id here?
  }
}

My question: how can I access the value of id in the implementation of the identityMacro.impl macro? I have tried passing it as an extra argument to macroTransform but this does not work. I assume I have to access it via the Context?