处理的11个阶段
| POST_HEAD | realip |
| SERVER_REWRITE | rewrite |
| FIND_CONFIG | |
| REWRITE | rewrite |
| POST_REWRITE | |
| PREACCESS | limit_conn, limit_req |
| ACCESS | auth_basic ,access, auth_request |
| POST_ACCESS | |
| PRECONTENT | try_files |
| CONTENT | index， autoindex , concat |
| LOG | accesslog |
11 个阶段的顺序处理