express-session 可以不用 cookie-parser
原來的程式除了 express-session， 又重複設定了自用 cookie/gen_session()， 不必要的複雜結構與資源的浪費，刪除！
Cookie options
Note Since version 1.5.0, the cookie-parser middleware no longer needs to be used for this module to work. This module now directly reads and writes cookies on req/res. Using cookie-parser may result in issues if the secret is not the same between this module and cookie-parser.
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