tsk-3: Add Token support (#10)

Closes #3

Reviewed-on: phoenix/textsender-api#10
Co-authored-by: phoenix <kundeng00@pm.me>
Co-committed-by: phoenix <kundeng00@pm.me>

internal/services/jwt_service.go

@@ -0,0 +1,50 @@
+package services
+
+import (
+	"time"
+
+	"github.com/golang-jwt/jwt/v5"
+
+	txtmodels_token "git.kundeng.us/phoenix/textsender-models/pkg/token"
+	txtmodels_user "git.kundeng.us/phoenix/textsender-models/pkg/user"
+)
+
+type JWTService struct {
+	secretKey []byte
+}
+
+func NewJWTService(secretKey string) *JWTService {
+	return &JWTService{
+		secretKey: []byte(secretKey),
+	}
+}
+
+func (s *JWTService) ValidateToken(tokenString string) (*txtmodels_user.User, error) {
+	// TODO: Include more user information in the claims to populate user
+	claims := &txtmodels_token.Claims{}
+
+	token, err := jwt.ParseWithClaims(tokenString, claims, func(token *jwt.Token) (interface{}, error) {
+		// Validate the signing method
+		if _, ok := token.Method.(*jwt.SigningMethodHMAC); !ok {
+			return nil, jwt.ErrSignatureInvalid
+		}
+		return s.secretKey, nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	if !token.Valid {
+		return nil, jwt.ErrSignatureInvalid
+	}
+
+	// Check token expiration
+	if time.Now().After(claims.ExpiresAt.Time) {
+		return nil, jwt.ErrTokenExpired
+	}
+
+	return &txtmodels_user.User{
+		Id: claims.UserId,
+	}, nil
+}