[server] Token 검증 함수 템플릿 작성

> ### ISSUE
> * Group: `server`
> * Type: `feature`
> * Detail: 매 요청마다 토큰을 검증할 필요가 있기 때문에 토큰을 검증하는 함수를 아예 템플릿화 해 분리
>
> ### TODO
> 1. [x] Token verify method templete 작성
>
> ### Estimated time
>
> ### `0.5h`
>
> ### Labels
> * Estimated time: `E: 0.5h`
> * Group : `server`
> * Sprint: `Sprint__1__`
> * Urgency: `Low`

The issue names the server group and a token-verification function template but provides no file, test, or entry point. Locate the server authentication code first, then confirm the intended function boundary; done means the reusable token-verification template described in the issue is present.

Written by the indexing model from the issue text.