feat: add token validation and auto-refresh functionality in frontend helpers

backend/app/routers/auth.py

@@ -4,6 +4,9 @@ import uuid
 from fastapi import APIRouter, HTTPException, status
 from jose import JWTError
 
+from fastapi import Depends
+
+from ..dependencies import get_current_user
 from ..models.auth import LoginRequest, RefreshRequest, RegisterRequest, TokenResponse
 from ..services.auth import (
     authenticate_user,
@@ -95,3 +98,11 @@ async def logout(body: RefreshRequest) -> None:
     jti = payload.get("jti", "")
     if jti:
         await revoke_refresh_token(jti)
+
+
+@router.get("/validate")
+async def validate(
+    current_user: dict = Depends(get_current_user),
+) -> dict:
+    """Return the token payload if the access token is valid."""
+    return current_user