Apply mapping to symbols returned from dynamic CSP sources

Previously if a dynamic source returned a symbol such as :self it
would be converted to a string implicity, e.g:

  policy.default_src -> { :self }

would generate the header:

  Content-Security-Policy: default-src self

and now it generates:

  Content-Security-Policy: default-src 'self'

1 files changed, 2 insertions, 1 deletions

diff --git a/actionpack/lib/action_dispatch/http/content_security_policy.rb b/actionpack/lib/action_dispatch/http/content_security_policy.rb
index 50953e32b5..15b7bd1233 100644
--- a/actionpack/lib/action_dispatch/http/content_security_policy.rb
+++ b/actionpack/lib/action_dispatch/http/content_security_policy.rb
@@ -257,7 +257,8 @@ module ActionDispatch #:nodoc:
           if context.nil?
             raise RuntimeError, "Missing context for the dynamic content security policy source: #{source.inspect}"
           else
-            context.instance_exec(&source)
+            resolved = context.instance_exec(&source)
+            resolved.is_a?(Symbol) ? apply_mapping(resolved) : resolved
           end
         else
           raise RuntimeError, "Unexpected content security policy source: #{source.inspect}"