module Sprockets::Rails::Helper

def secure_subresource_integrity_context?

http://www.w3.org/TR/SRI/#non-secure-contexts-remain-non-secure
Only serve integrity metadata for HTTPS requests: 
def secure_subresource_integrity_context?
  respond_to?(:request) && self.request && (self.request.local? || self.request.ssl?)
end