Add JWT authentication

- Create register and login use cases
- Implement JWT service for token generation and validation
- Add authentication middleware to protect habit endpoints
- Create auth HTTP handlers (register, login)
- Update habit handlers to extract userID from JWT token
- Register/login endpoints: POST /auth/register, POST /auth/login
- Habit endpoints now require Bearer token in Authorization header
- Tested: register -> create habit -> list habits works correctly

internal/infrastructure/http/auth_handlers.go

@@ -0,0 +1,118 @@
+package http
+
+import (
+	"encoding/json"
+	"net/http"
+
+	"habit-tracker-api/internal/application/commands"
+	"habit-tracker-api/internal/application/queries"
+	"habit-tracker-api/internal/infrastructure/auth"
+	"habit-tracker-api/internal/shared/errors"
+)
+
+type AuthHandlers struct {
+	registerHandler *commands.RegisterUserHandler
+	loginHandler    *queries.LoginUserHandler
+	jwtService      *auth.JWTService
+}
+
+func NewAuthHandlers(
+	registerHandler *commands.RegisterUserHandler,
+	loginHandler *queries.LoginUserHandler,
+	jwtService *auth.JWTService,
+) *AuthHandlers {
+	return &AuthHandlers{
+		registerHandler: registerHandler,
+		loginHandler:    loginHandler,
+		jwtService:      jwtService,
+	}
+}
+
+type RegisterRequest struct {
+	Email    string `json:"email"`
+	Password string `json:"password"`
+	Timezone string `json:"timezone"`
+}
+
+type LoginRequest struct {
+	Email    string `json:"email"`
+	Password string `json:"password"`
+}
+
+type AuthResponse struct {
+	Token  string `json:"token"`
+	UserID string `json:"user_id"`
+}
+
+func (h *AuthHandlers) Register(w http.ResponseWriter, r *http.Request) {
+	var req RegisterRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		respondError(w, http.StatusBadRequest, "Invalid request body")
+		return
+	}
+
+	cmd := commands.RegisterUserCommand{
+		Email:    req.Email,
+		Password: req.Password,
+		Timezone: req.Timezone,
+	}
+
+	userID, err := h.registerHandler.Handle(r.Context(), cmd)
+	if err != nil {
+		if err == errors.ErrInvalidInput {
+			respondError(w, http.StatusBadRequest, "Invalid email or password (min 8 characters)")
+			return
+		}
+		if err == errors.ErrAlreadyExists {
+			respondError(w, http.StatusConflict, "Email already registered")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "Failed to register user")
+		return
+	}
+
+	token, err := h.jwtService.GenerateToken(userID, req.Email)
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "Failed to generate token")
+		return
+	}
+
+	respondJSON(w, http.StatusCreated, AuthResponse{
+		Token:  token,
+		UserID: userID,
+	})
+}
+
+func (h *AuthHandlers) Login(w http.ResponseWriter, r *http.Request) {
+	var req LoginRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		respondError(w, http.StatusBadRequest, "Invalid request body")
+		return
+	}
+
+	query := queries.LoginUserQuery{
+		Email:    req.Email,
+		Password: req.Password,
+	}
+
+	result, err := h.loginHandler.Handle(r.Context(), query)
+	if err != nil {
+		if err == errors.ErrNotFound || err == errors.ErrInvalidInput {
+			respondError(w, http.StatusUnauthorized, "Invalid email or password")
+			return
+		}
+		respondError(w, http.StatusInternalServerError, "Failed to login")
+		return
+	}
+
+	token, err := h.jwtService.GenerateToken(result.UserID, result.Email)
+	if err != nil {
+		respondError(w, http.StatusInternalServerError, "Failed to generate token")
+		return
+	}
+
+	respondJSON(w, http.StatusOK, AuthResponse{
+		Token:  token,
+		UserID: result.UserID,
+	})
+}