Create signed urls for CloudFront with Ruby

Question

History:

1. I created a key and pem file on Amazon.
2. I created a private bucket
3. I created a public distribution and used origin id to connect to the private bucket: works
4. I created a private distribution and connected it the same as #3 - now I get access denied: expected

I'm having a really hard time generating a url that will work. I've been trying to follow the directions described here: http://docs.amazonwebservices.com/AmazonCloudFront/latest/DeveloperGuide/index.html?PrivateContent.html

This is what I've got so far... doesn't work though - still getting access denied:

def url_safe(s)
  s.gsub('+','-').gsub('=','_').gsub('/','~').gsub(/\n/,'').gsub(' ','')
end

def policy_for_resource(resource, expires = Time.now + 1.hour)
  %({"Statement":[{"Resource":"#{resource}","Condition":{"DateLessThan":{"AWS:EpochTime":#{expires.to_i}}}}]})
end

def signature_for_resource(resource, key_id, private_key_file_name, expires = Time.now + 1.hour)
    policy = url_safe(policy_for_resource(resource, expires))
    key = OpenSSL::PKey::RSA.new(File.readlines(private_key_file_name).join("")) 
    url_safe(Base64.encode64(key.sign(OpenSSL::Digest::SHA1.new, (policy))))
end

def expiring_url_for_private_resource(resource, key_id, private_key_file_name, expires = Time.now + 1.hour)
  sig = signature_for_resource(resource, key_id, private_key_file_name, expires)
  "#{resource}?Expires=#{expires.to_i}&Signature=#{sig}&Key-Pair-Id=#{key_id}"
end

resource = "http://d27ss180g8tp83.cloudfront.net/iwantu.jpeg"
key_id = "APKAIS6OBYQ253QOURZA"
pk_file = "doc/pk-APKAIS6OBYQ253QOURZA.pem"
puts expiring_url_for_private_resource(resource, key_id, pk_file)

Can anyone tell me what I'm doing wrong here?

Answer 1

All,

I just created a small gem that can be used to sign CF URLs with Ruby using some of the code from this question:

https://github.com/stlondemand/aws_cf_signer

I will probably be making significant changes to it over the coming weeks as I try to actually use it in my application but wanted to let you all know as you are listed in the attributions section. :)

Thank you!

Answer 2

remove url_safe before you set policy: policy = policy_for_resource(resource, expires)

according to docs only Base64 should be safe Url-Safe (m) = CharReplace( Base64(m), "+=/", "-_~" )

.. and make sure that CloudFront is configured properly like: http://blog.cloudberrylab.com/2010/03/how-to-configure-private-content-for.html

Answer 3

Yep, leaving policy as policy = policy_for_resource(resource, expires) worked for me.

Answer 4

I forked right_aws (they haven't responded to my pull request)... I set up cloudfront private streaming and downloads in their acf library: http://github.com/wiseleyb/right_aws

Answer 5

I agree with Dylan. He did good work with signing urls. I had the same issue. I went through the docs. There is one thing that I didn't find there. When you create a private distribution, then you usually give access for files, bucket, etc...

I got Access Denied errors until I assigned Bucket Policy.

You can assign policy like:

{
    "Version":"2008-10-17",
    "Id":"PolicyForCloudFrontPrivateContent",
    "Statement":[{
            "Sid":" Grant a CloudFront Origin Identity access to support private content",
            "Effect":"Allow",
            "Principal":{
            "CanonicalUser":"here-goes-your-canonical-name-you-attached-to-cloudfront79a59df900b949e55d96a1e698fbacedfd6e09d98eacf8f8d5218e7cd47ef2be"
            },
            "Action":"s3:GetObject",
            "Resource":"arn:aws:s3:::change-me-to-your-bucketname/*"
        }
    ]
}