Merge pull request #993 from dhermes/fix-983

Documenting exclusion of GCE for generate_signed_url.

gcloud/credentials.py

@@ -301,6 +301,13 @@ def generate_signed_url(credentials, resource, expiration,
                         content_type=None):
     """Generate signed URL to provide query-string auth'n to a resource.
 
+    .. note::
+      If you are on Google Compute Engine, you can't generate a signed URL.
+      Follow https://github.com/GoogleCloudPlatform/gcloud-python/issues/922
+      for updates on this. If you'd like to be able to generate a signed URL
+      from GCE, you can use a standard service account from a JSON file
+      rather than a GCE service account.
+
     :type credentials: :class:`oauth2client.appengine.AppAssertionCredentials`
     :param credentials: Credentials object with an associated private key to
                         sign text.

gcloud/storage/blob.py

@@ -157,6 +157,14 @@ def generate_signed_url(self, expiration, method='GET',
                             client=None, credentials=None):
         """Generates a signed URL for this blob.
 
+        .. note::
+          If you are on Google Compute Engine, you can't generate a signed URL.
+          Follow
+              https://github.com/GoogleCloudPlatform/gcloud-python/issues/922
+          for updates on this. If you'd like to be able to generate a signed
+          URL from GCE, you can use a standard service account from a JSON
+          file rather than a GCE service account.
+
         If you have a blob that you want to allow access to for a set
         amount of time, you can use this method to generate a URL that
         is only valid within a certain time period.