To discover whether your Object Storage system supports this feature, check with your service provider or send a GET request using the /info path.
A temporary URL gives users temporary access to objects. For example, a website might want to provide a link to download a large object in Object Storage, but the Object Storage account has no public access. The website can generate a URL that provides time-limited GET access to the object. 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.
Ask your cloud administrator to enable the temporary URL feature. For information, see TempURL in the Source Documentation.
To use POST requests to upload objects to specific Object Storage locations, use Form POST middleware instead of temporary URL middleware.
A temporary URL is comprised of the URL for an object with added query parameters:
Example Temporary URL format
https://swift-cluster.example.com/v1/my_account/container/object
?temp_url_sig=da39a3ee5e6b4b0d3255bfef95601890afd80709
&temp_url_expires=1323479485
&filename=My+Test+File.pdf
The example shows these elements:
Object URL: Required. The full path URL to the object.
temp_url_sig: Required. An HMAC-SHA1 cryptographic signature that defines the allowed HTTP method, expiration date, full path to the object, and the secret key for the temporary URL.
temp_url_expires: Required. An expiration date as a UNIX Epoch timestamp, which is an integer value. For example, 1390852007 represents Mon, 27 Jan 2014 19:46:47 GMT.
For more information, see Epoch & Unix Timestamp Conversion Tools.
filename: Optional. Overrides the default file name. Object Storage generates a default file name for GET temporary URLs that is based on the object name. Object Storage returns this value in the Content-Disposition response header. Browsers can interpret this file name value as a file attachment to be saved.
The cryptographic signature used in Temporary URLs and also in Form POST middleware uses a secret key. Object Storage allows you to store two secret key values per account, and two per container. When validating a request, Object Storage checks signatures against all keys. Using two keys at each level enables key rotation without invalidating existing temporary URLs.
To set the keys at the account level, set one or both of the following request headers to arbitrary values on a POST request to the account:
To set the keys at the container level, set one or both of the following request headers to arbitrary values on a POST or PUT request to the container:
The arbitrary values serve as the secret keys.
For example, use the swift post command to set the secret key to ``MYKEY``:
$ swift post -m "Temp-URL-Key:MYKEY"
Changing these headers invalidates any previously generated temporary URLs within 60 seconds, which is the memcache time for the key.
Temporary URL middleware uses an HMAC-SHA1 cryptographic signature. This signature includes these elements:
This sample Python code shows how to compute a signature for use with temporary URLs:
Example HMAC-SHA1 signature for temporary URLs
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/my_account/container/object'
key = 'MYKEY'
hmac_body = '%s\n%s\n%s' % (method, expires, path)
signature = hmac.new(key, hmac_body, sha1).hexdigest()
Do not URL-encode the path when you generate the HMAC-SHA1 signature. However, when you make the actual HTTP request, you should properly URL-encode the URL.
The ``MYKEY`` value is one of the key values as described in Secret Keys.
For more information, see RFC 2104: HMAC: Keyed-Hashing for Message Authentication.
Object Storage provides the swift-temp-url script that auto-generates the ``temp_url_sig`` and ``temp_url_expires`` query parameters. For example, you might run this command:
$ bin/swift-temp-url GET 3600 /v1/my_account/container/object MYKEY
This command returns the path:
/v1/my_account/container/object
?temp_url_sig=5c4cc8886f36a9d0919d708ade98bf0cc71c9e91
&temp_url_expires=1374497657
To create the temporary URL, prefix this path with the Object Storage storage host name. For example, prefix the path with https://swift-cluster.example.com, as follows:
https://swift-cluster.example.com/v1/my_account/container/object
?temp_url_sig=5c4cc8886f36a9d0919d708ade98bf0cc71c9e91
&temp_url_expires=1374497657