Permission(ACL) middleware for Multer that acts based on multipart/form-data parameters - node.js

Question

In my Express.js REST API, I'm using multer to upload images into server's static folder with diskStorage. I have wanted to build a generic file upload page for both users and admins. Detailed use case is as follows:
choose a category from a drop-down list
write an valid id in the form field,
choose a valid image(file) and submit.
if regular user (with isAdmin==false) selects category different than users , then the API responds with a 403 and won't upload the image at all.
What I want to achieve is to allow only users with isAdmin==true to upload images for the all categories. But, within the same route, regular users can only upload images for the users category.
The question is how to get access to the req.body.category inside authentication & authorization middleware and reject upload process pre-flight?
I need to check category and isAdmin fields at the same time to make decision about giving permission for upload process or not.
React-side
const formData = new FormData()
formData.append('id', this.state.id)
formData.append('category', this.state.category)
formData.append('photo', this.state.file)
this.props.fileUpload(formData)
Express-side
Router
router.post('/upload', AuthController.role('admin'), UploadController.uploadPhoto);
AuthController
public static role(role: any) {
return (req: Request, res: Response, next: NextFunction) => {
if (role === 'admin') {
console.dir(req.body); // req.body prints { user_id: 1, isAdmin: true }
// cannot decide whether give access to the route or not over here because we don't know the req.body.category yet.
if (req.body && req.body.isAdmin) {
next();
} else {
return res.status(403).send(new Unauthorized());
}
}
};
}
UploadController
const imageFilter = (req, file, cb) => {
console.dir(req.body); // prints { id: '1', category: 'users' } cannot access req.body.isAdmin over here
if (!file.originalname.match(/\.(jpg|jpeg|png|gif)$/)) {
return cb(new Error('Only image files are allowed!'), false);
}
cb(null, true);
};
const upload = util.promisify(multer({ storage, fileFilter: imageFilter, limits: {fileSize: MAX_SIZE} })
.single('photo'));
export class UploadController {
public static async uploadPhoto(req: any, res: Response, next: NextFunction) {
// req.body.isAdmin is available over here
try {
await upload(req, res);
imageUrl = `${HOST}/static/${req.file.filename}`;
} catch (e) {
return res.status(400).send(new BadRequest('Image upload operation is not successful.'));
}
}
UPDATE: My current workaround solution is to save the image temporarily and then check the category and isAdmin at the same time when they become available.
try {
await upload(req, res);
....
..
// Now req.body.category and req.body.isAdmin are both available here
}