You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: rsapkcs1_algorithm.rb
    path of file: ./repos/webauthn-ruby/lib/cose
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require "cose"
require "cose/algorithm/sign
    
  def to_pkey(key)
    case key
    when COSE::Key::RSA
      key.to_pkey
    when OpenSSL::PKey::RSA
      key
    else
      raise(COSE::Error, "Incompatible key for algorithm")
    end