common-grpc: authClient.projectId is not guaranteed to be defined

[ofrobots]

Discovered this while investigating #2125.

common-grpc:service.js:

GrpcService.prototype.getGrpcCredentials_ = function(callback) {
  var self = this;

  this.authClient.getAuthClient(function(err, authClient) {
    if (err) {
      callback(err);
      return;
    }

    var credentials = grpc.credentials.combineChannelCredentials(
      grpc.credentials.createSsl(),
      grpc.credentials.createFromGoogleCredential(authClient)
    );

    if (!self.projectId || self.projectId === '{{projectId}}') {
      self.projectId = authClient.projectId;                  // <<<<<<<<<
    }

authClient.projectId is not guaranteed to be defined. Unless I am mistaken, only JWTClient would have this property. This means that auto-detection of credentials is not working with gRPC based client libraries unless the user provides the projectId manually?

[stephenplusplus]

I actually discovered the same and addressed it as part of #2100 by getting the project ID from self.authClient.projectId, the google-auto-auth instance property, set here: https://github.com/stephenplusplus/google-auto-auth/blob/2a03c3c9894b44715cae9e67784042d18daceda9/index.js#L87. It seems not all google-auth-library auth client instances have the projectId as a property, but it will return the projectId as a third argument to the getApplicationDefault callback. That's the one google-auto-auth sets on its instance as projectId.

This means that auto-detection of credentials is not working with gRPC based client libraries unless the user provides the projectId manually?

This is true for our APIs that use gax APIs*, but not ones that use gRPC directly through common.GrpcService. This is more a question of environment rather than transport mechanism. If google-auth-library (not google-auto-auth) is working as expected, the callback to getApplicationDefault() will return a projectId if one was detected.

* as we convert, this will be addressed (see a solution in #2072).

[lukesneeringer]

It looks like @stephenplusplus is already on this. I was not very clear on the priority based on the description; feel free to change if you think I got it wrong.

[stephenplusplus]

Fixed by #2100.