json: trim payload before checking it

Author: gbrlsnchs

json.go

@@ -1,10 +1,14 @@
 package jwt
 
-import "errors"
+import (
+	"bytes"
+	"errors"
+)
 
 // ErrNotJSONObject is the error for when a JWT payload is not a JSON object.
 var ErrNotJSONObject = errors.New("jwt: payload is not a valid JSON object")
 
 func isJSONObject(payload []byte) bool {
+	payload = bytes.TrimSpace(payload)
 	return payload[0] == '{' && payload[len(payload)-1] == '}'
 }