Add caching of get_auth call in Swift

Should make calls significantly faster for our Swift customers

Fixes https://jira.prod.coreos.systems/browse/QS-39

storage/test/test_swift.py

@@ -8,6 +8,7 @@ from mock import MagicMock
 
 from storage import StorageContext
 from storage.swift import SwiftStorage
+from swiftclient.client import ClientException
 
 base_args = {
   'context': StorageContext('nyc', None, None, None, None),
@@ -27,18 +28,26 @@ class MockSwiftStorage(SwiftStorage):
     return self._connection
 
 class FakeSwiftStorage(SwiftStorage):
-  def __init__(self, fail_checksum=False, connection=None, *args, **kwargs):
+  def __init__(self, fail_checksum=False,connection=None, *args, **kwargs):
     super(FakeSwiftStorage, self).__init__(*args, **kwargs)
-    self._connection = connection or FakeSwift(fail_checksum=fail_checksum)
+    self._connection = connection or FakeSwift(fail_checksum=fail_checksum,
+                                               temp_url_key=kwargs.get('temp_url_key'))
 
   def _get_connection(self):
     return self._connection
 
 
 class FakeSwift(object):
-  def __init__(self, fail_checksum=False):
+  def __init__(self, fail_checksum=False, temp_url_key=None):
     self.containers = defaultdict(dict)
     self.fail_checksum = fail_checksum
+    self.temp_url_key = temp_url_key
+
+  def get_auth(self):
+    if self.temp_url_key == 'exception':
+      raise ClientException('I failed!')
+      
+    return 'http://fake/swift', None
 
   def head_object(self, container, path):
     return self.containers[container].get(path)
@@ -258,3 +267,13 @@ def test_empty_chunks_queued_for_deletion():
 
   found2 = chunk_cleanup_queue.get()
   assert found2 is None
+
+@pytest.mark.parametrize('temp_url_key, expects_url', [
+  (None, False),
+  ('foobarbaz', True),
+  ('exception', False),
+])
+def test_get_direct_download_url(temp_url_key, expects_url):
+  swift = FakeSwiftStorage(temp_url_key=temp_url_key, **base_args)
+  swift.put_content('somepath', 'hello world!')
+  assert (swift.get_direct_download_url('somepath') is not None) == expects_url