code: public static SSECustomerKey generateSSECustomerKeyForPresignUrl(
              String algorithm) {
          if (algorithm == null)
              throw new IllegalArgumentException();
          return new SSECustomerKey().withAlgorithm(algorithm);
      }
docs: Constructs a new SSECustomerKey that can be used for generating the
  presigned URL's.
  
  Currently, "AES256" is the only supported algorithm.
  
  @see SSEAlgorithm#AES256
  
  @param algorithm
  The server-side encryption algorithm to use with this
  customer-provided server-side encryption key; must not be
  null.
  
  @throws IllegalArgumentException
  if the input parameter is null.