uploads_controller.rb

class UploadsController < ApplicationController
  before_action :require_login

  def auth
    date_stamp = Date.strptime(params[:datetime], "%Y%m%dT%H%M%SZ").strftime("%Y%m%d")
    secret_key = "AWS_SECRET_KEY"
    aws_region = "us-east-1" # << set to your region

    date_key = OpenSSL::HMAC.digest("sha256", "AWS4" + secret_key, date_stamp)
    region_key = OpenSSL::HMAC.digest("sha256", date_key, aws_region)
    service_key = OpenSSL::HMAC.digest("sha256", region_key, "s3")
    signing_key = OpenSSL::HMAC.digest("sha256", service_key, "aws4_request")

    render plain: OpenSSL::HMAC.hexdigest("sha256", signing_key, params[:to_sign]).gsub("\n", "")
  end

end