Google cloud storage is it ok to expose API key?

Question

I'm developing an application which lets users upload pictures. I'd like to use Google cloud services to store these pictures. I am creating a unique GUID for each image in database and would like to store the images in the cloud with that name. It makes sense for me to make an ajax request for a GUID and then upload the image from the same page directly to google cloud services.

https://github.com/GoogleCloudPlatform/storage-getting-started-javascript/blob/master/index.html

Like shown in this example.

My first question is, should I be sending this to my back-end(C# code) and uploading it from there? Or is this the correct approach?

And my second question if this is the correct approach is, wouldn't exposing my details like that in javascript allow other people to upload from outside my application as well?

Answer 1

An API key, by itself, identifies a call as being associated with a certain project for purposes of billing. It's only necessary for anonymous calls. An API key does not grant any sort of authorizations. If there's an object in a bucket in your project that only your project members can see, the API key won't give anyone permission to read it.

That said, it's not a great idea to share your API key if you can help it, and if you need to share it, you should lock it down as much as possible. API keys can be limited to use with only certain IP addresses, only with certain web referrers (for instance, it will only work with JavaScript clients on www.yoursite.com), or only when run from a particular iPhone or Android app. These precautions aren't cryptographically fool-proof (there's no reason a hacker couldn't spoof a referer header), but they do make them pretty much useless for someone else who just wants to paste an API key somewhere to enable a web app and doesn't want to pay for it themselves.

The problem with using the javascript client's approach for your application is that individual users would either end up uploading objects completely anonymously or with their own Google accounts. Neither is super great, since the anonymous option would basically require you to create a bucket with anonymous writes enabled, and you don't want to do that.

There is a great approach to letting users upload pictures, though: signed URLs. Signed URLs allow your server to securely sign, in advance, a request to upload an object with your credentials. This is your best option for letting anonymous end users securely upload objects to your buckets.

Documentation on signed URLs: https://cloud.google.com/storage/docs/accesscontrol#Signed-URLs