Alright, let's get started with securing those file uploads in Supabase storage. First things first, if you haven't already, sign in to Supabase and create a new project. Once you're in, head over to the project dashboard.

Next, click on the "Storage" tab in your Supabase dashboard. Here, you'll want to create a new storage bucket. Give it a unique name and a little description.

When you're setting up that storage bucket, make sure to turn off the "Public" access option. This way, only authorized users can upload or download files. Keeps things nice and secure.

Now, head over to the "Auth" section and enable Row Level Security (RLS) for the tables linked to your file storage. You can create custom policies to control who gets access. For instance, create an RLS policy that allows only authenticated users to insert into the storage objects:

CREATE POLICY "Insert objects" ON storage.objects FOR INSERT
  USING (auth.role() = 'authenticated');

Next up, go to the "API" tab and scroll down to the "Client Libraries" section. Copy the API key and endpoint URL provided. You'll need these for your frontend app to interact with the storage bucket securely.

Time to install the Supabase client library in your frontend application:

npm install @supabase/supabase-js

Then, initialize the Supabase client with the API key and endpoint URL:

import { createClient } from '@supabase/supabase-js';

const supabaseUrl = 'https://xyzcompany.supabase.co';
const supabaseKey = 'your-anon-key';
const supabase = createClient(supabaseUrl, supabaseKey);

Now, let's get that file upload logic going in your frontend app:

async function uploadFile(file) {
  const user = supabase.auth.user();
  if (user) {
    const { data, error } = await supabase.storage
      .from('your-bucket-name')
      .upload(`public/${user.id}/${file.name}`, file);

    if (error) {
      console.error('Error uploading file:', error);
    } else {
      console.log('File uploaded successfully:', data);
    }
  } else {
    console.error('User not authenticated');
  }
}

Before you upload, always validate the file type and size on the client side. This ensures only allowed file types and sizes are uploaded. For example:

function validateFile(file) {
  const allowedTypes = ['image/jpeg', 'image/png', 'application/pdf'];
  const maxSize = 5 * 1024 * 1024; // 5 MB

  if (!allowedTypes.includes(file.type)) {
    throw new Error('Unsupported file type');
  }
  if (file.size > maxSize) {
    throw new Error('File size exceeds limit');
  }
  return true;
}

Then, handle the file upload function incorporating the validation:

async function uploadValidatedFile(file) {
  try {
    validateFile(file);
    await uploadFile(file);
    console.log('File upload complete');
  } catch (error) {
    console.error('Validation or upload failed:', error.message);
  }
}

Finally, keep an eye on the storage bucket's access logs and usage reports from the Supabase dashboard. This helps you spot any suspicious activities and maintain the integrity of your file storage.

By following these steps, you can secure file uploads in Supabase storage effectively.