Merge lp:~marix/duplicity/azure-storage-sas into lp:~duplicity-team/duplicity/0.8-series

[Matthias Bach]

This branch adds support for Shared Access Signature to the Azure backend which allows to run Duplicity with a minimal set of permissions.

The currently supported access method, using an account key, grants Duplicity full administrative permissions on that Azure storage account. However, there is a fairly low limit on the number of storage account that can be used within a single storage subscription, thus it is not necessarily optimal to create a separate one for each single system that requires backup. In addition, this also grants a lot of unnecessary powers to the system running Duplicity.

Share Access Signatures allow to grant a specific set of permissions of permissions on a storage account, or a single container. To test you need to create a shared access signature including read, write and deletion permissions on the container. Then run duplicity passing the shared access signature in the environment variable AZURE_SHARED_ACCESS_SIGNATURE. The AZURE_ACCOUNT_NAME is also still required, but the AZURE_ACCOUNT_KEY is no longer necessary.

=== modified file 'bin/duplicity.1'
--- bin/duplicity.1	2017-01-30 21:46:37 +0000
+++ bin/duplicity.1	2017-02-14 09:50:31 +0000
@@ -1543,9 +1543,13 @@
 .B REQUIREMENTS
 above.
 
-It uses two environment variables for authentification:
+It uses environment variables for authentification:
 .BR AZURE_ACCOUNT_NAME " (required),"
-.BR AZURE_ACCOUNT_KEY " (required)"
+.BR AZURE_ACCOUNT_KEY " (optional),
+.BR AZURE_SHARED_ACCESS_SIGNATURE " (optional)."
+One of
+.BR AZURE_ACCOUNT_KEY " or"
+.BR AZURE_SHARED_ACCESS_SIGNATURE " is required."
 
 A container name must be a valid DNS name, conforming to the following naming
 rules:

=== modified file 'duplicity/backends/azurebackend.py'
--- duplicity/backends/azurebackend.py	2016-05-11 21:07:04 +0000
+++ duplicity/backends/azurebackend.py	2017-02-14 09:50:31 +0000
@@ -51,15 +51,23 @@
             raise BackendException('Azure backend requires Microsoft Azure Storage SDK for Python '
                                    '(https://pypi.python.org/pypi/azure-storage/).')
 
+        # TODO: validate container name
+        self.container = parsed_url.path.lstrip('/')
+
         if 'AZURE_ACCOUNT_NAME' not in os.environ:
             raise BackendException('AZURE_ACCOUNT_NAME environment variable not set.')
-        if 'AZURE_ACCOUNT_KEY' not in os.environ:
-            raise BackendException('AZURE_ACCOUNT_KEY environment variable not set.')
-        self.blob_service = BlobService(account_name=os.environ['AZURE_ACCOUNT_NAME'],
-                                        account_key=os.environ['AZURE_ACCOUNT_KEY'])
-
-        # TODO: validate container name
-        self.container = parsed_url.path.lstrip('/')
+
+        if 'AZURE_ACCOUNT_KEY' in os.environ:
+            self.blob_service = BlobService(account_name=os.environ['AZURE_ACCOUNT_NAME'],
+                                            account_key=os.environ['AZURE_ACCOUNT_KEY'])
+            self._create_container()
+        elif 'AZURE_SHARED_ACCESS_SIGNATURE' in os.environ:
+            self.blob_service = BlobService(account_name=os.environ['AZURE_ACCOUNT_NAME'],
+                                            sas_token=os.environ['AZURE_SHARED_ACCESS_SIGNATURE'])
+        else:
+            raise BackendException('Neither AZURE_ACCOUNT_KEY nor AZURE_SHARED_ACCESS_SIGNATURE environment variable not set.')
+
+    def _create_container(self):
         try:
             self.blob_service.create_container(self.container, fail_on_exist=True)
         except self.AzureConflictError: