gochat/backend/internal/auth/jwt.go

package auth

import (
	"errors"
	"fmt"
	"time"

	"github.com/golang-jwt/jwt/v5"

	"github.com/gochat/gochat/internal/config"
	"github.com/gochat/gochat/internal/model"
)

// Reference: P2E §1.2 — JWT Claims structure
// Replaces Chatwoot's DeviseTokenAuth multi-token mechanism with single JWT + Refresh token.

// Claims represents JWT token claims.
type Claims struct {
	UserID       uint   `json:"user_id"`
	AccountID    uint   `json:"account_id"`     // current active account
	Role         string `json:"role"`            // agent/administrator/custom_role
	Provider     string `json:"provider"`        // email/google/saml
	CustomRoleID uint   `json:"custom_role_id,omitempty"` // enterprise custom role
	jwt.RegisteredClaims
}

// TokenPair holds an access token and refresh token.
type TokenPair struct {
	AccessToken  string    `json:"access_token"`
	RefreshToken string    `json:"refresh_token"`
	ExpiresAt    time.Time `json:"expires_at"`
}

// JWTService provides JWT token generation and validation.
type JWTService struct {
	cfg *config.JWTConfig
}

// NewJWTService creates a JWT service with configuration.
func NewJWTService(cfg *config.JWTConfig) *JWTService {
	return &JWTService{cfg: cfg}
}

// GenerateTokenPair generates an access token + refresh token pair.
// Access Token: 15min expiry with full Claims
// Refresh Token: 7 days expiry, only UserID + Provider
func (s *JWTService) GenerateTokenPair(user *model.User, accountID uint, role string) (*TokenPair, error) {
	// Access Token
	accessExpiry := time.Now().Add(time.Duration(s.cfg.ExpiryHours) * time.Hour)
	accessClaims := &Claims{
		UserID:       user.ID,
		AccountID:    accountID,
		Role:         role,
		Provider:     user.Provider,
		CustomRoleID: func() uint { if user.CustomRoleID != nil { return *user.CustomRoleID }; return 0 }(),
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(accessExpiry),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			Subject:   fmt.Sprintf("user_%d", user.ID),
			Issuer:    "gochat",
		},
	}

	accessToken := jwt.NewWithClaims(jwt.SigningMethodHS256, accessClaims)
	accessTokenString, err := accessToken.SignedString([]byte(s.cfg.Secret))
	if err != nil {
		return nil, fmt.Errorf("failed to sign access token: %w", err)
	}

	// Refresh Token
	refreshExpiry := time.Now().Add(time.Duration(s.cfg.RefreshExpiryHours) * time.Hour)
	refreshClaims := &Claims{
		UserID:   user.ID,
		Provider: user.Provider,
		RegisteredClaims: jwt.RegisteredClaims{
			ExpiresAt: jwt.NewNumericDate(refreshExpiry),
			IssuedAt:  jwt.NewNumericDate(time.Now()),
			Subject:   fmt.Sprintf("refresh_%d", user.ID),
			Issuer:    "gochat",
		},
	}

	refreshToken := jwt.NewWithClaims(jwt.SigningMethodHS256, refreshClaims)
	refreshTokenString, err := refreshToken.SignedString([]byte(s.cfg.Secret))
	if err != nil {
		return nil, fmt.Errorf("failed to sign refresh token: %w", err)
	}

	return &TokenPair{
		AccessToken:  accessTokenString,
		RefreshToken: refreshTokenString,
		ExpiresAt:    accessExpiry,
	}, nil
}

// ValidateAccessToken validates an access JWT token and returns claims.
func (s *JWTService) ValidateAccessToken(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, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
		}
		return []byte(s.cfg.Secret), nil
	})

	if err != nil {
		return nil, fmt.Errorf("failed to parse token: %w", err)
	}

	claims, ok := token.Claims.(*Claims)
	if !ok || !token.Valid {
		return nil, errors.New("invalid token claims")
	}

	// Verify it's an access token (not a refresh token)
	if claims.Subject != fmt.Sprintf("user_%d", claims.UserID) {
		return nil, errors.New("invalid token type: expected access token")
	}

	return claims, nil
}

// ValidateRefreshToken validates a refresh JWT token and returns claims.
func (s *JWTService) ValidateRefreshToken(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, fmt.Errorf("unexpected signing method: %v", token.Header["alg"])
		}
		return []byte(s.cfg.Secret), nil
	})

	if err != nil {
		return nil, fmt.Errorf("failed to parse refresh token: %w", err)
	}

	claims, ok := token.Claims.(*Claims)
	if !ok || !token.Valid {
		return nil, errors.New("invalid refresh token claims")
	}

	// Verify it's a refresh token
	if claims.Subject != fmt.Sprintf("refresh_%d", claims.UserID) {
		return nil, errors.New("invalid token type: expected refresh token")
	}

	return claims, nil
}

// RefreshAccessToken generates a new access token from a valid refresh token.
func (s *JWTService) RefreshAccessToken(refreshTokenString string, accountID uint, role string) (*TokenPair, error) {
	claims, err := s.ValidateRefreshToken(refreshTokenString)
	if err != nil {
		return nil, err
	}

	// Generate new token pair with the user ID from refresh claims
	// Note: we need the full user object for GenerateTokenPair, but we only have claims here
	// In production, we fetch user from DB using claims.UserID
	user := &model.User{
		Base:     model.Base{ID: claims.UserID},
		Provider: claims.Provider,
	}

	return s.GenerateTokenPair(user, accountID, role)
}