使用certbot无法生成证书，出现以下错误：
org.shredzone.acme4j.exception.AcmeException: Failed to pass the challenge for domain www.
mysampledomain123.com, ... Giving up.
我手动检查了挑战文件并得到
http://www.mysampledomain123.com/.well-known/acme-challenge/jU--PkDrn5tDZw2RN6NNJHbPD00ovHFkLFvN3mJdeQX
在文件内部：
jU--PkDrn5tDZw2RN6NNJHbPD00ovHFkLFvN3mJdeQX.tuMr-UijwpsJ1KVZkdWTYgodWZ2SxxKdB7_CMAAEfpg
这是完整的HTTP响应标头：
Accept-Ranges: bytes
Connection: keep-alive
Content-Encoding: gzip
Content-Type: text/plain;charset=iso-8859-1
Date: Sun, 16 Feb 2020 14:15:22 GMT
Server: nginx/1.14.0 (Ubuntu)
Transfer-Encoding: chunked
Vary: Accept-Charset, Accept-Encoding, Accept-Language, Accept
X-Powered-By: MyServer
X-RateLimit-Limit: 1000
X-RateLimit-Remaining: 999
X-RateLimit-Reset: 0
我想知道问题出在HTTP响应标头还是内容本身。 任何想法，将不胜感激。