I have downloaded FontAwesome using npm and then copied the css-file and the fonts into the right folders in the root-diretory of my electron-application using grunts copy t
I faced same issue, using API Gateway to serve static font-files on Amazon S3.
I fixed it by adding */* as Binary Media Types on the AWS Console.
More information on binary media types management on https://docs.aws.amazon.com/apigateway/latest/developerguide/api-gateway-payload-encodings-configure-with-console.html