google-cloud-storage allows users to generate signed URLs via the signUrl method. However, it currently doesn't allow users to supply additional query parameters to be included with the URL.

This isn't as big of an issue for V2 as it is for V4 signing. For V2 URLs, you can just add/remove/alter params after the URL has been generated - the V2 signing spec doesn't use query params when calculating the signature. But for V4 signed URLs, the params are canonical; they're used when creating the signature and the set of params cannot be altered after the signature is calculated. This means you can't do certain operations with V4 signed URLs today (e.g. listing objects in a bucket that start with a given prefix, since the prefix must be specified via query param).

Corresponding internal issue tracker:
https://issuetracker.google.com/issues/145017709

@frankyn