Snippet from an S3 download/upload client based purely on spray-client

S3Signing.scala

  /**
   * Amazon S3 uploads and downloads need to have an authorization header containing a signature based on a very specific formatting
   * of several of the headers of the HTTP request. This method only implements the parts that are required for our use cases,
   * thus very specific situations like headers spanning multiple lines are not supported.
   * For the details of the string-to-sign that is constructed see http://docs.aws.amazon.com/AmazonS3/latest/dev/RESTAuthentication.html?r=1821
   */
  def signAwsRequest(method: String, dateString: String, contentType: String, bucket: String, resource: String, amzHeaders: List[HttpHeader] = List.empty[HttpHeader], contentMd5: String = ""): String = {
    val bucketResource = s"/$bucket$resource"

    val signableAmzHeaders = amzHeaders.sortBy(_.name).map { header ⇒
      s"""${header.name}:${header.value}"""
    }
    val signatureElements = method :: contentMd5 :: contentType :: dateString :: signableAmzHeaders ::: bucketResource :: Nil
    val stringToSign = signatureElements.mkString("\n")

    calculateHmacSha1(filesSettings.S3.SecretKey, stringToSign).asBase64String
  }