Headers can be read from stdin?

I have a use case where I'd the headers to be able to be read from stdin, in particular I'm passing credentials through the headers and I don't want the credentials to show up as command line parameters which exposes the credentials.

Would it be possible to allow the headers to be read from stdin like the request data? _I could put in a PR if this is simple, would you accept it?_

I was thinking of putting a switch like this for reading from stdin just like the request data: https://github.com/fullstorydev/grpcurl/blob/master/cmd/grpcurl/grpcurl.go#L489