頻繁に使う時期があったので、2.5.1のソースをgrepして、$_SERVER変数を調べた。以下にキー名を残しておく。

CONTENT_LENGTH
CONTENT_TYPE
DOCUMENT_ROOT
HTTPS
HTTP_ACCEPT_ENCODING
HTTP_AUTHORIZATION
HTTP_HOST
HTTP_IF_MODIFIED_SINCE
HTTP_IF_NONE_MATCH
HTTP_REFERER
HTTP_SLUG
HTTP_TITLE
HTTP_USER_AGENT
HTTP_X_ORIGINAL_URL
HTTP_X_REWRITE_URL
PATH_INFO
PATH_TRANSLATED
PHP_AUTH_PW
PHP_AUTH_USER
PHP_SELF
QUERY_STRING
REMOTE_ADDR
REQUEST_METHOD
REQUEST_URI
SCRIPT_FILENAME
SCRIPT_NAME
SERVER_NAME
SERVER_SOFTWARE
https