UT middleware with authentication and fileOverrides

I am trying to have a middleware in one of my upload routes where I authenticate a user and I want to add a customId to the upload. I can do one or the other but when I try to do both in the same middleware function I get a 500 error.

This is the code snippet, in this case user logs a correct object but then throws a 500 server error.
export const ourFileRouter = {
// Define as many FileRoutes as you like, each with a unique routeSlug
imageUploader: f({ image: { maxFileSize: "4MB", maxFileCount: 10 } })
.middleware(async ({ req, files }) => {
const user = await auth(req);
console.log("User in UT middleware", user);
if (!user) throw new UploadThingError("Unauthorized");

const fileOverrides = files.map((file) => {
const myIdentifier = file.name;
return { ...file, customId: myIdentifier };
});

return { foo: "bar" as const, [UTFiles]: fileOverrides };
})
.onUploadComplete(async ({ metadata, file }) => {
metadata;
file.customId;
}),
} satisfies FileRouter;

Does anybody know what I am missing here?
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