class Aws::S3::PresignedPost

def policy(datetime)
  check_required_values!
  policy = {}
  policy['expiration'] = @signature_expiration.utc.iso8601
  policy['conditions'] = @conditions.dup
  signature_fields(datetime).each do |name, value|
    policy['conditions'] << { name => value }
  end
  base64(Json.dump(policy))
end