def topics
      if universal?
        ext = extension(UNIVERSAL_CERTIFICATE_EXTENSION)
        seq = OpenSSL::ASN1.decode(OpenSSL::ASN1.decode(ext.to_der).value[1].value)
        seq.select.with_index { |_, index| index.even? }.map(&:value)
      else
        [app_bundle_id]
      end
    end
def topics
      if universal?
        ext = extension(UNIVERSAL_CERTIFICATE_EXTENSION)
        seq = OpenSSL::ASN1.decode(OpenSSL::ASN1.decode(ext.to_der).value[1].value)
        seq.select.with_index { |_, index| index.even? }.map(&:value)
      else
        [app_bundle_id]
      end
    end
@return [Array<String>]
         a list of ‘topics’ that the certificate supports.

 @see https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Chapters/APNsProviderAPI.html