class_docstr: Initialises the authenticator.
  
  :param gcp_key: name of the key to use for authentication (see GCP_*_KEY values)
  :param project_extra: optional extra project parameter passed to google cloud
         connection
class_docstr_tok: ["Initialises","the","authenticator",".",":","param","gcp_key",":","name","of","the","key","to","use","for","authentication","(","see","GCP_","*","_KEY","values",")",":","param","project_extra",":","optional","extra","project","parameter","passed","to","google","cloud","connection"]
code: def _validate_key_set(self):
      if self.full_key_path is None:
          raise AirflowException("The gcp_key is not set!")
      if not os.path.isfile(self.full_key_path):
          raise AirflowException(
              f"The key {self.gcp_key} could not be found. Please copy it to the {self.full_key_path} path."
          )
  
imports: from __future__ import annotations
  import json
  import os
  import subprocess
  from airflow import settings
  from airflow.exceptions import AirflowException
  from airflow.models import Connection
  from tests.test_utils import AIRFLOW_MAIN_FOLDER
  from tests.test_utils.logging_command_executor import CommandExecutor
label_desc: Use image node_id 6 for calling the GcpAuthenticator obj's underlying member method code with example usage: obj._validate_key_set() without return types