[Feature] Kakao OAuth login

[fregataa]

Summary

Implement Kakao OAuth login for user authentication.

Prerequisites

• [Feature] OAuth infrastructure setup #20 OAuth infrastructure setup

Scope

Setup

• Create Kakao Developers application
• Configure Kakao Login settings
• Set redirect URI
• Request necessary scopes (email, profile)

Backend

• Add Kakao OAuth config (REST API key, secret)
• Implement Kakao OAuth callback handler
• Exchange authorization code for access token
• Fetch user info from Kakao API

Frontend

• Add "카카오로 로그인" button (with Kakao brand guidelines)
• Handle Kakao OAuth redirect

Environment Variables

KAKAO_CLIENT_ID=
KAKAO_CLIENT_SECRET=
KAKAO_REDIRECT_URI=

Acceptance Criteria

• Users can sign up/login with Kakao account
• Kakao account linked to user profile
• Follows Kakao brand guidelines for login button

References

• Kakao Login Documentation