Improve secret handling in SignStream

Refactor secret assignment logic in SignStream constructor.

Author: panva

lib/sign-stream.js

@@ -34,7 +34,12 @@ function jwsSign(opts) {
 }
 
 function SignStream(opts) {
-  var secret = opts.secret||opts.privateKey||opts.key;
+  var secret = opts.secret;
+  secret = secret == null ? opts.privateKey : secret;
+  secret = secret == null ? opts.key : secret;
+  if (/^hs/i.test(opts.header.alg) === true && secret == null) {
+    throw new TypeError('secret must be a string or buffer or a KeyObject')
+  }
   var secretStream = new DataStream(secret);
   this.readable = true;
   this.header = opts.header;