add Basic Auth.

set ENABLE_AUTH flag to enable it.

refer to commits below:
- https://github.com/siklol/Wikitten/commit/c0ce80d07f9b1bf40de96c3e4c51354d28298f53
- https://github.com/siklol/Wikitten/commit/740a161ddc28ed87628d26a5edc6106d90c784b4