Add support for Content-Security-Policy

A nonce-based Content-Security-Policy thwarts XSS attacks by allowing
inline JavaScript to execute if the script nonce matches the header
value. Rails 5.2 supports nonce-based Content-Security-Policy headers,
so provide configuration to enable this and make it work.

To support this, we need to change all `:javascript` HAML filters to the
following form:

```
= javascript_tag nonce: true do
  :plain
    ...
```

We use `%script` throughout our HAML to store JSON and other text, but
since this doesn't execute, browsers don't appear to block this content
from being used and require the nonce value to be present.

1 files changed, 8 insertions, 8 deletions

diff --git a/app/views/layouts/errors.html.haml b/app/views/layouts/errors.html.haml
index 06069a72951..74484005b48 100644
--- a/app/views/layouts/errors.html.haml
+++ b/app/views/layouts/errors.html.haml
@@ -8,12 +8,12 @@
   %body
     .page-container
       = yield
-    -# haml-lint:disable InlineJavaScript
-    :javascript
-      (function(){
-        var goBackElement = document.querySelector('.js-go-back');
+    = javascript_tag nonce: true do
+      :plain
+        (function(){
+          var goBackElement = document.querySelector('.js-go-back');
 
-        if (goBackElement && history.length > 1) {
-          goBackElement.style.display = 'block';
-        }
-      }());
+          if (goBackElement && history.length > 1) {
+            goBackElement.style.display = 'block';
+          }
+        }());