How do i add custom id in uploadthing?

import { createUploadthing, type FileRouter } from "uploadthing/next";
import { UploadThingError } from "uploadthing/server";

const f = createUploadthing();

const auth = (req: Request) => ({ id: "fakeId" }); // Fake auth function

export const ourFileRouter = {
  imageUploader: f({ image: { maxFileSize: "4MB" } })
    .middleware(async ({ req }) => {
      const user = await auth(req);
      if (!user) throw new UploadThingError("Unauthorized");
      return { userId: user.id };
    })
    .onUploadComplete(async ({ metadata, file }) => {
      console.log("Upload complete for userId:", metadata.userId);
      console.log("file url", file.url);
      return { uploadedBy: metadata.userId };
    }),
} satisfies FileRouter;

export type OurFileRouter = typeof ourFileRouter;

      <UploadButton
        endpoint="imageUploader"
        onClientUploadComplete={(res) => {
          // Do something with the response
          console.log("Files: ", res);
          alert("Upload Completed");
        }}
        onUploadError={(error: Error) => {
          // Do something with the error.
          alert(`ERROR! ${error.message}`);
        }}
      />