Gem::Package#setup_signer

# File tmp/rubies/ruby-3.1.3/lib/rubygems/package.rb, line 562
def setup_signer(signer_options: {})
  passphrase = ENV["GEM_PRIVATE_KEY_PASSPHRASE"]
  if @spec.signing_key
    @signer =
      Gem::Security::Signer.new(
        @spec.signing_key,
        @spec.cert_chain,
        passphrase,
        signer_options
      )

    @spec.signing_key = nil
    @spec.cert_chain = @signer.cert_chain.map {|cert| cert.to_s }
  else
    @signer = Gem::Security::Signer.new nil, nil, passphrase
    @spec.cert_chain = @signer.cert_chain.map {|cert| cert.to_pem } if
      @signer.cert_chain
  end
end