`ServiceOptions.java`: Extract projectId from credentials when provided via .setCredentials`

[jabubake]

Handwritten clients that use ServiceOptions:

when .setCredentials is used, the project id is not extracted from the service account.
This behavior is different when service account credentials are supplied via GOOGLE_APPLICATION_CREDENTIALS env var (project id is extracted)

https://github.com/GoogleCloudPlatform/google-cloud-java/blob/master/google-cloud-clients/google-cloud-core/src/main/java/com/google/cloud/ServiceOptions.java#L465

Similar issue for BigQuery:
GoogleCloudPlatform/java-docs-samples#936

[jabubake]

@hostirosti FYI

[hostirosti]

Example:

GoogleCredentials creds;
try {
   InputStream is = MyClass.class.getClassLoader().getResourceAsStream("service_account.json");
   creds = GoogleCredentials.fromStream(is);
} catch (IOException e) {
   e.printStackTrace();
   return;
}

ServiceOptions.newBuilder().setCredentials(creds)...

[yihanzhen]

ServiceOptions sets projectId and credentials separately. It would first look for projectId in this sequence, and then look for credentials in this sequence. The reason you have the same projectId when you set the credentials through GOOGLE_APPLICATION_CREDENTIALS is that this json file is the first place ServiceOptions looks for both projectId and credentials if neither of them is set explicitly.

Though there has been discussions over whether we should extract the projectId from a ServiceAccountCredentials when the credentials is explicitly passed to the ServiceOptions, we generally consider the current behavior intended. Besides, it is possible that users might want the projectId to be different from what is provided in the ServiceAccountCredentials json file.

We encourage people to use GOOGLE_APPLICATION_CREDENTIALS environment variable over other authentication approaches whenever possible. If you have to manually create and set a credentials, please also set the projectId:

ServiceOptions options = ServiceOptions.newBuilder()
    .setCredentials(credentials)
    .setProjectId("[project-id]")
    .build();