feat: add challenge to auth service

internal/usecase/auth_service.go

@@ -1 +1,49 @@
 package usecase
+
+import (
+	"backend/internal/domain"
+	"context"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/google/uuid"
+)
+
+type AuthService interface {
+	GenerateChallenge(ctx context.Context, pubKey string) (*domain.Challenge, error)
+}
+
+type authService struct {
+	userRepo        *domain.UserRepo
+	sessionRepo     *domain.SessionRepo
+	challengeExp    uint
+	tokenExp        uint
+	refreshTokenExp uint
+}
+
+func NewAuthService(
+	userRepo *domain.UserRepo,
+	sessionRepo *domain.SessionRepo,
+	challengeExp uint,
+	tokenExp uint,
+	refreshTokenExp uint) AuthService {
+	return &authService{
+		userRepo:        userRepo,
+		sessionRepo:     sessionRepo,
+		challengeExp:    challengeExp,
+		tokenExp:        tokenExp,
+		refreshTokenExp: refreshTokenExp,
+	}
+}
+
+func (s *authService) GenerateChallenge(ctx context.Context, pubKey string) (*domain.Challenge, error) {
+	if !common.IsHexAddress(pubKey) {
+		return nil, domain.ErrWalletInvalid
+	}
+	challenge := &domain.Challenge{
+		Message:   uuid.New(),
+		TimeStamp: time.Now().UTC(),
+		ExpiresAt: time.Now().Add(time.Duration(s.challengeExp) * time.Minute),
+	}
+	return challenge, nil
+}