Temporary URL

Allows the creation of URLs to provide temporary access to objects. For example, a website may wish to provide a link to download a large object in OpenStack Object Storage, but the Object Storage account has no public access. The website can generate a URL that provides GET access for a limited time to the resource. When the web browser user clicks on the link, the browser downloads the object directly from Object Storage, eliminating the need for the website to act as a proxy for the request. If the user shares the link with all his friends, or accidentally posts it on a forum, the direct access is limited to the expiration time set when the website created the link.

A temporary URL is the typical URL associated with an object, with two additional query parameters:

An example of a temporary URL:

    https://swift-cluster.example.com/v1/AUTH_a422b2-91f3-2f46-74b7-d7c9e8958f5d30/container/object?
    temp_url_sig=da39a3ee5e6b4b0d3255bfef95601890afd80709&
    temp_url_expires=1323479485

To create temporary URLs, first set the X-Account-Meta-Temp-URL-Key header on your Object Storage account to an arbitrary string. This string serves as a secret key. For example, to set a key of b3968d0207b54ece87cccc06515a89d4 using the swift command-line tool:

$ swift post -m "Temp-URL-Key:b3968d0207b54ece87cccc06515a89d4"

Next, generate an HMAC-SHA1 (RFC 2104) signature to specify:

Here is code generating the signature for a GET for 24 hours on /v1/AUTH_account/container/object:

import hmac
from hashlib import sha1
from time import time
method = 'GET'
duration_in_seconds = 60*60*24
expires = int(time() + duration_in_seconds)
path = '/v1/AUTH_a422b2-91f3-2f46-74b7-d7c9e8958f5d30/container/object'
key = 'mykey'
hmac_body = '%s\n%s\n%s' % (method, expires, path)
sig = hmac.new(key, hmac_body, sha1).hexdigest()
s = 'https://{host}/{path}?temp_url_sig={sig}&temp_url_expires={expires}'
url = s.format(host='swift-cluster.example.com', path=path, sig=sig, expires=expires)

Any alteration of the resource path or query arguments results in a 401 Unauthorized error. Similarly, a PUT where GET was the allowed method returns a 401. HEAD is allowed if GET or PUT is allowed. Using this in combination with browser form post translation middleware could also allow direct-from-browser uploads to specific locations in Object Storage.

	Note
	Changing the X-Account-Meta-Temp-URL-Key invalidates any previously generated temporary URLs within 60 seconds (the memcache time for the key). Object Storage supports up to two keys, specified by X-Account-Meta-Temp-URL-Key and X-Account-Meta-Temp-URL-Key-2. Signatures are checked against both keys, if present. This is to allow for key rotation without invalidating all existing temporary URLs.

Opject Storage includes a script called swift-temp-url that generates the query parameters automatically:

$ bin/swift-temp-url GET 3600 /v1/AUTH_account/container/object mykey
/v1/AUTH_account/container/object?
temp_url_sig=5c4cc8886f36a9d0919d708ade98bf0cc71c9e91&
temp_url_expires=1374497657

Because this command only returns the path, you must prefix the Object Storage host name (for example, https://swift-cluster.example.com).

With GET Temporary URLs, a Content-Disposition header is set on the response so that browsers interpret this as a file attachment to be saved. The file name chosen is based on the object name, but you can override this with a filename query parameter. The following example specifies a filename of My Test File.pdf:

https://swift-cluster.example.com/v1/AUTH_a422b2-91f3-2f46-74b7-d7c9e8958f5d30/container/object?
temp_url_sig=da39a3ee5e6b4b0d3255bfef95601890afd80709&
temp_url_expires=1323479485&
filename=My+Test+File.pdf

To enable Temporary URL functionality, edit /etc/swift/proxy-server.conf to add tempurl to the pipeline variable defined in the [pipeline:main] section. The tempurl entry should appear immediately before the authentication filters in the pipeline, such as authtoken, tempauth or keystoneauth. For example:

[pipeline:main]
pipeline = pipeline = healthcheck cache tempurl authtoken keystoneauth proxy-server