fix: accept lowercase env vars (#578)

Author: JustinBeckwith

src/auth/googleauth.ts

@@ -288,7 +288,8 @@ export class GoogleAuth {
  */
  async _tryGetApplicationCredentialsFromEnvironmentVariable(
  options?: RefreshOptions): Promise<JWT|UserRefreshClient|null> {
- const credentialsPath = process.env['GOOGLE_APPLICATION_CREDENTIALS'];
+ const credentialsPath = process.env['GOOGLE_APPLICATION_CREDENTIALS'] ||
+ process.env['google_application_credentials'];
  if (!credentialsPath || credentialsPath.length === 0) {
  return null;
  }
@@ -583,7 +584,9 @@ export class GoogleAuth {
  * @api private
  */
  private getProductionProjectId() {
- return process.env['GCLOUD_PROJECT'] || process.env['GOOGLE_CLOUD_PROJECT'];
+ return process.env['GCLOUD_PROJECT'] ||
+ process.env['GOOGLE_CLOUD_PROJECT'] || process.env['gcloud_project'] ||
+ process.env['google_cloud_project'];
  }
 
  /**