def thumbprint(digest_type = nil)
      digest_type ||= 'SHA256'
      thumbprint_binary = JOSE.encode(to_thumbprint_map)
      return JOSE.urlsafe_encode64(OpenSSL::Digest.new(digest_type).digest(thumbprint_binary))
    end
def thumbprint(digest_type = nil)
      digest_type ||= 'SHA256'
      thumbprint_binary = JOSE.encode(to_thumbprint_map)
      return JOSE.urlsafe_encode64(OpenSSL::Digest.new(digest_type).digest(thumbprint_binary))
    end
Returns the unique thumbprint for a {JOSE::JWK JOSE::JWK} using the `digest_type`.

 @see JOSE::JWK.thumbprint
 @see https://tools.ietf.org/html/rfc7638 RFC 7638 - JSON Web Key (JWK) Thumbprint
 @param [String] digest_type
 @return [String]