[Task] Back-End 유저 정보 확인 모듈 구현

> ### ISSUE
> * Group: `server`
> * Type: `feature`
> * Detail: 로그인 방식에 따라서, 이메일, 유저네임, 비밀번호 일치여부를 Boolean값으로 응답하는 모듈 구현
>
> ### TODO
> 1. [ ] 파라미터로 사용할것들: loginMethod, email, uesername, password
> 2. [ ] 리턴되는 값의 종류: Boolean
>

> * Estimated time: `E: 0.5h`
> * Group : `server`
> * Urgency: `High`

The issue identifies a server-side feature but names no file, entry point, or test; begin by locating the server module responsible for login-method handling. Done means the module accepts loginMethod, email, username, and password and returns a Boolean indicating whether the supplied user information matches the selected login method.

Written by the indexing model from the issue text.