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How to remove or edit a Shared Access Signature from Windows Azure

Until now we saw how we can create a Shared Access Signature for blobs, table and queues. In real life scenario, this is not all the think that we do. After we create a Shared Access Signature we want to be able to edit or remove it.
In this blog post we will look over some common scenario that can appear when we work with Shared Access Signature.
The first scenario is when we want to remove the access to a resources using Shared Access Signature. After we created an access signature and we shared with the client, maybe we realize that we send the access signature to the wrong user for example. For this case we want to delete the access signature from the permissions list. For this cased is very important to have stored (or to be able to recreate) the name of permissions that we created. If you remember, when we create an access policy we set a unique name for each policy. Based on this name we can remove any access policy that we created.
Blobs, tables and queues have a method named “GetPermissions()”. For each given type, this method returns the permissions for the given type. Based on the name we can access each access policy and remove them.
CloudTable myTable = …
TablePermissions permissions = myTable.GetPermissions();
var accessPolicies = permissions.SharedAccessPolicies;
accessPolicies.Remove(“myAccessPolicyName”);
permissions.SetPermissions(permissions);
In this example, we extracted from our Azure table the TablePermissions for our table. From this object we need to extract the SharedAccessPolicies list. This object contains the list of all Shared Access Policies of our table. Based on the name of the access policy we removed our item from the list. At this step is very important to update the permissions list of our table (if we want to persistent the changes). Because of this we need to call the “SetPermissions” method and give us parameter the list of permissions.
The same method will be used for queues and blogs. Each of this items contains the GetPermissions() method.
Another scenario that is very often used is to change the Shared Access Policies for a given client. For example if we share some data from a table in a form of monthly subscription, we don’t want to send a new access token every month to the client. Because of this we want to be able to update the expiration data every month.
The implementation of this scenario is very similar to one before. We don’t want to remove the policy, the only think that we want is to get an instance to our policy and change the expiration time interval.
In this post we saw how we can remove or edit an access policy. In the next post will talk about how Shared Access Signature looks, how the flow looks like when a access policy is created and about some best practices that are need to be followed when we use them.
Tutorials about Shared Access Signature:
  1. Overview
  2. How to use Shared Access Signature with tables from Windows Azure
  3. How to use Shared Access Signature with blobs from Windows Azure
  4. How to use Shared Access Signature with queues from Windows Azure
  5. How to remove or edit a Shared Access Signature from Windows Azure 
  6. Some scenarios when we can use Shared Access Signature from Windows Azure

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