根据http://httpd.apache.org/docs/2.2/mod/mod_proxy.html#x-headers, X-Forwarded-Host 可以包含多个值:
Be careful when using these headers on the origin server, since they will contain more than one (comma-separated) value if the original request already contained one of these headers
REMOTE_HOST 可以包含多个值吗?或者它总是单一的价值?