Presigned URL to download objects from S3

s3_url.rb

require "openssl"
require "base64"

access_key = ".........."
secret_key = "..................."
s3_object = "$BUCKET/$PATH"

expires = (Time.now + 300).to_i   # 5 minutes

data = %[GET\n\n\n#{expires}\n/#{s3_object}]

digest = OpenSSL::Digest.new('sha1')
hmac = OpenSSL::HMAC.digest(digest, secret_key, data)
signature = Base64.urlsafe_encode64(hmac)

puts "https://s3.amazonaws.com/#{s3_object}?AWSAccessKeyId=#{access_key}&Signature=#{signature}&Expires=#{expires}"