class JSON::JWK

def to_rsa_key
  e, n, d, p, q, dp, dq, qi = [:e, :n, :d, :p, :q, :dp, :dq, :qi].collect do |key|
    if self[key]
      OpenSSL::BN.new Base64.urlsafe_decode64(self[key]), 2
    end
  end
  # Public key
  data_sequence = OpenSSL::ASN1::Sequence([
    OpenSSL::ASN1::Integer(n),
    OpenSSL::ASN1::Integer(e),
  ])
  if d && p && q && dp && dq && qi
    data_sequence = OpenSSL::ASN1::Sequence([
      OpenSSL::ASN1::Integer(0),
      OpenSSL::ASN1::Integer(n),
      OpenSSL::ASN1::Integer(e),
      OpenSSL::ASN1::Integer(d),
      OpenSSL::ASN1::Integer(p),
      OpenSSL::ASN1::Integer(q),
      OpenSSL::ASN1::Integer(dp),
      OpenSSL::ASN1::Integer(dq),
      OpenSSL::ASN1::Integer(qi),
    ])
  end
  asn1 = OpenSSL::ASN1::Sequence(data_sequence)
  OpenSSL::PKey::RSA.new(asn1.to_der)
end