class Aws::S3::EncryptionV2::KmsCipherProvider

def build_encryption_context(cek_alg, options = {})
  kms_context = (options[:kms_encryption_context] || {})
    .each_with_object({}) { |(k, v), h| h[k.to_s] = v }
  if kms_context.include? 'aws:x-amz-cek-alg'
    raise ArgumentError, 'Conflict in reserved KMS Encryption Context ' \
      'key aws:x-amz-cek-alg. This value is reserved for the S3 ' \
      'Encryption Client and cannot be set by the user.'
  end
  {
    'aws:x-amz-cek-alg' => cek_alg
  }.merge(kms_context)
end