Possible bug: Config option signingEndpoint is not used when passed to getSignedUrl

[MisanthropicBit]

I'm using the @google-cloud/storage library to implement an integration test for some code that uses signed urls (via file.getSignedUrl) and I'm testing with a bunch of test servers. In order to test signed urls I'm passing a custom signingEndpoint that points to a local test server that is started up when the test starts.

The problem is that the file.getSignedUrl seems to have a bug where that config option is not passed down through the code (here). If you follow the code down through URLSigner.getSignedUrl to URLSigner.getSignedUrlV4, you'll eventually get to this code which looks for the signingEndpoint in the config but never finds it. Effectively, the config option is ignored. The URLSigner.getSignedUrlV2 suffers from the same issue although I'm only using version 4.

I think this is a bug because the GetSignedUrlConfig interface includes a signingEndpoint option which is never used and I expected the provided signingEndpoint config option to be used in place of a default one.

A simple solution would be the following diff:

    const signConfig: SignerGetSignedUrlConfig = {
      method,
      expires: cfg.expires,
      accessibleAt: cfg.accessibleAt,
      extensionHeaders,
      queryParams,
      contentMd5: cfg.contentMd5,
      contentType: cfg.contentType,
      host: cfg.host,
+     signingEndpoint: cfg.signingEndpoint,
    };

If this is not a bug, what is the point of signingEndpoint? Does it do something else? Can I redirect the signing process to another endpoint in another way? My code will run in a GCE environment so this is only an issue for testing and if someone else needs to use a custom signing endpoint in a production environment in the future.

I've confirmed the issue in my tests (where authentication is done through test servers so the code will be allowed to eventually run the code in question), but I may simply be misunderstanding something here.