如何将Windows Azure SAS密钥作为客户端解析到期日期？

Question

I'm trying to check on the expiration date of the SAS key on the client side so that I can request a new SAS key once it expires. I'm using the Microsoft.WindowsAzure.Storage namespace (which is version 2.0 of the azure storage library). Is there a built in method for this or will I have to parse it manually?

Answer 1

I don't believe there's anything specific in the storage client library. You should be able to parse the querystring on the URI and look at the UTC date in signedexpiry . You can parse the querystring with HttpUtility.ParseQueryString() .

Here are two caveats to think about:

• This check won't be entirely accurate, since there could be clock-drift between your machine's clock and the Storage service's clock.
• If the server uses a shared access policy (which allows for programmatic modification/revocation of access), there's no guarantee that signedexpiry will be part of the querystring. More on shared access policies here .

Answer 2

David's answer is correct for the question about how to parse the expiry time (+1). But ultimately you should not be doing this. There are two better options:

1. The client should attempt to access the resource and then handle the authentication failure by requesting a new SAS.
2. Provide a method for the client to determine the SAS expiry time, and the client would then keep track of this time and do a refresh at some interval before the expiry. An example of this is shown at http://blogs.msdn.com/b/windowsazurestorage/archive/2012/06/12/introducing-table-sas-shared-access-signature-queue-sas-and-update-to-blob-sas.aspx .