CentOS7 YUM代理驗證失敗

Question

我偶然發現我的 CentOS7 伺服器有一個小問題。它是代理後面的虛擬伺服器，可以連接到互聯網，但不能使用 yum。每當我嘗試時，我都會收到錯誤：

Could not retrieve mirrorlist http://mirrorlist.centos.org/? 
release=7&arch=x86_64&repo=os&infra=stock error was
14: HTTP Error 407 - Proxy Authentication Required

即使我配置了代理/etc/環境：

http_proxy='http://user:password@url:8088/'
HTTP_PROXY='http://user:password@url:8088/'
https_proxy='http://user:password@url:8088/'
HTTPS_PROXY='http://user:password@url:8088/'
ftp_proxy='http://user:password@url:8088/'
FTP_PROXY='http://user:password@url:8088/'
no_proxy='localhost,127.0.0.1,localaddress,*.localdomain.com,*.bl.ch,10.*'
NO_PROXY='localhost,127.0.0.1,localaddress,*.localdomain.com,*.bl.ch,10.*'

並在/etc/yum.conf：

proxy=http://url:8088/
proxy_username=user_name
proxy_password=password

我甚至在/root/.bash_profile：

export http_proxy="http://url:8088/"

並在/etc/wgetrc：

 http_proxy='http://user:password@url:8088/'
 HTTP_PROXY='http://user:password@url:8088/'
 https_proxy='http://user:password@url:8088/'
 HTTPS_PROXY='http://user:password@url:8088/'
 ftp_proxy='http://user:password@url:8088/'
 FTP_PROXY='http://user:password@url:8088/'
 no_proxy='localhost,127.0.0.1,localaddress,*.localdomain.com,*.bl.ch,10.*'
 NO_PROXY='localhost,127.0.0.1,localaddress,*.localdomain.com,*.bl.ch,10.*'

我真的不明白它怎麼仍然缺少身份驗證；有人知道如何解決這個問題嗎？