quite a lot of things

internal/auth/auth.go

@@ -0,0 +1,211 @@
+package auth
+
+import (
+	"crypto/rand"
+	"encoding/hex"
+	"errors"
+	"net/http"
+	"os"
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+	"golang.org/x/crypto/bcrypt"
+)
+
+var (
+	ErrInvalidCredentials = errors.New("invalid email or password")
+	ErrInvalidToken       = errors.New("invalid or expired token")
+	ErrUserNotFound       = errors.New("user not found")
+	ErrUserExists         = errors.New("user already exists")
+)
+
+// Config holds auth configuration
+type Config struct {
+	JWTSecret     []byte
+	CookieDomain  string
+	CookieSecure  bool
+	TokenDuration time.Duration
+}
+
+// User represents an authenticated user
+type User struct {
+	ID             string `json:"id"`
+	Email          string `json:"email"`
+	Password       string `json:"-"` // Never expose password hash
+	CompanyDetails string `json:"company_details"`
+	BankDetails    string `json:"bank_details"`
+	CreatedAt      string `json:"created_at"`
+}
+
+// Claims represents JWT claims
+type Claims struct {
+	UserID string `json:"user_id"`
+	Email  string `json:"email"`
+	jwt.RegisteredClaims
+}
+
+// Service handles authentication
+type Service struct {
+	config Config
+	users  UserStore
+}
+
+// UserStore interface for user persistence
+type UserStore interface {
+	CreateUser(email, passwordHash string) (*User, error)
+	GetUserByEmail(email string) (*User, error)
+	GetUserByID(id string) (*User, error)
+}
+
+// NewService creates a new auth service
+func NewService(users UserStore) *Service {
+	secret := os.Getenv("JWT_SECRET")
+	if secret == "" {
+		// Generate a random secret if not provided (not recommended for production)
+		b := make([]byte, 32)
+		rand.Read(b)
+		secret = hex.EncodeToString(b)
+	}
+
+	domain := os.Getenv("COOKIE_DOMAIN")
+	secure := os.Getenv("COOKIE_SECURE") == "true"
+
+	return &Service{
+		config: Config{
+			JWTSecret:     []byte(secret),
+			CookieDomain:  domain,
+			CookieSecure:  secure,
+			TokenDuration: 24 * time.Hour,
+		},
+		users: users,
+	}
+}
+
+// HashPassword hashes a password using bcrypt with high cost
+func HashPassword(password string) (string, error) {
+	// Use cost of 12 for good security/performance balance
+	hash, err := bcrypt.GenerateFromPassword([]byte(password), 12)
+	if err != nil {
+		return "", err
+	}
+	return string(hash), nil
+}
+
+// CheckPassword verifies a password against a hash
+func CheckPassword(password, hash string) bool {
+	err := bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
+	return err == nil
+}
+
+// Register creates a new user account
+func (s *Service) Register(email, password string) (*User, error) {
+	// Check if user exists
+	existing, _ := s.users.GetUserByEmail(email)
+	if existing != nil {
+		return nil, ErrUserExists
+	}
+
+	// Validate password strength
+	if len(password) < 8 {
+		return nil, errors.New("password must be at least 8 characters")
+	}
+
+	// Hash password
+	hash, err := HashPassword(password)
+	if err != nil {
+		return nil, err
+	}
+
+	return s.users.CreateUser(email, hash)
+}
+
+// Login authenticates a user and returns a JWT token
+func (s *Service) Login(email, password string) (string, error) {
+	user, err := s.users.GetUserByEmail(email)
+	if err != nil || user == nil {
+		return "", ErrInvalidCredentials
+	}
+
+	if !CheckPassword(password, user.Password) {
+		return "", ErrInvalidCredentials
+	}
+
+	return s.generateToken(user)
+}
+
+// generateToken creates a new JWT token for a user
+func (s *Service) generateToken(user *User) (string, error) {
+	now := time.Now()
+	claims := &Claims{
+		UserID: user.ID,
+		Email:  user.Email,
+		RegisteredClaims: jwt.RegisteredClaims{
+			ExpiresAt: jwt.NewNumericDate(now.Add(s.config.TokenDuration)),
+			IssuedAt:  jwt.NewNumericDate(now),
+			NotBefore: jwt.NewNumericDate(now),
+			Issuer:    "billit",
+			Subject:   user.ID,
+		},
+	}
+
+	token := jwt.NewWithClaims(jwt.SigningMethodHS256, claims)
+	return token.SignedString(s.config.JWTSecret)
+}
+
+// ValidateToken validates a JWT token and returns the claims
+func (s *Service) ValidateToken(tokenString string) (*Claims, error) {
+	token, err := jwt.ParseWithClaims(tokenString, &Claims{}, func(token *jwt.Token) (interface{}, error) {
+		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
+			return nil, ErrInvalidToken
+		}
+		return s.config.JWTSecret, nil
+	})
+
+	if err != nil {
+		return nil, ErrInvalidToken
+	}
+
+	if claims, ok := token.Claims.(*Claims); ok && token.Valid {
+		return claims, nil
+	}
+
+	return nil, ErrInvalidToken
+}
+
+// CreateAuthCookie creates an HTTP-only secure cookie for the token
+func (s *Service) CreateAuthCookie(token string) *http.Cookie {
+	return &http.Cookie{
+		Name:     "auth_token",
+		Value:    token,
+		Path:     "/",
+		Domain:   s.config.CookieDomain,
+		MaxAge:   int(s.config.TokenDuration.Seconds()),
+		HttpOnly: true,                  // Prevents JavaScript access
+		Secure:   s.config.CookieSecure, // Only send over HTTPS in production
+		SameSite: http.SameSiteStrictMode,
+	}
+}
+
+// ClearAuthCookie returns a cookie that clears the auth token
+func (s *Service) ClearAuthCookie() *http.Cookie {
+	return &http.Cookie{
+		Name:     "auth_token",
+		Value:    "",
+		Path:     "/",
+		Domain:   s.config.CookieDomain,
+		MaxAge:   -1,
+		HttpOnly: true,
+		Secure:   s.config.CookieSecure,
+		SameSite: http.SameSiteStrictMode,
+	}
+}
+
+// GetUserFromToken retrieves the user from a valid token
+func (s *Service) GetUserFromToken(tokenString string) (*User, error) {
+	claims, err := s.ValidateToken(tokenString)
+	if err != nil {
+		return nil, err
+	}
+
+	return s.users.GetUserByID(claims.UserID)
+}