Limit hostname labels to 63 chars max

63 octets is the maximum length a hostname label can be: https://en.wikipedia.org/wiki/Hostname#Syntax

aws4.js

@@ -78,7 +78,7 @@ function RequestSigner(request, credentials) {
 }
 
 RequestSigner.prototype.matchHost = function(host) {
-  var match = (host || '').match(/([^\.]+)\.(?:([^\.]*)\.)?amazonaws\.com(\.cn)?$/)
+  var match = (host || '').match(/([^\.]{1,63})\.(?:([^\.]{0,63})\.)?amazonaws\.com(\.cn)?$/)
   var hostParts = (match || []).slice(1, 3)
 
   // ES's hostParts are sometimes the other way round, if the value that is expected