Add editor link scheme to the CSP

Author: RobinDaugherty

lib/better_errors/editor.rb

@@ -84,6 +84,10 @@ def url(raw_path, line)
       url_proc.call(file, line)
     end
 
+    def scheme
+      url('/fake', 42).sub(/:.*/, ':')
+    end
+
     private
 
     attr_reader :url_proc

lib/better_errors/middleware.rb

@@ -122,6 +122,7 @@ def show_error_page(env, exception=nil)
           # Inline style is required by the syntax highlighter.
           "style-src 'self' 'unsafe-inline'",
           "connect-src 'self'",
+          "navigate-to 'self' #{BetterErrors.editor.scheme}",
         ].join('; '),
       }