def __post_init__(self) -> BigQueryCredentialsConfig:
    """Validate that either credentials or client ID/secret are provided."""
    if not self.credentials and (not self.client_id or not self.client_secret):
      raise ValueError(
          "Must provide either credentials or client_id and client_secret pair."
      )
    if self.credentials and (
        self.client_id or self.client_secret or self.scopes
    ):
      raise ValueError(
          "Cannot provide both existing credentials and"
          " client_id/client_secret/scopes."
      )

    if self.credentials:
      self.client_id = self.credentials.client_id
      self.client_secret = self.credentials.client_secret
      self.scopes = self.credentials.scopes

    if not self.scopes:
      self.scopes = BIGQUERY_DEFAULT_SCOPE

    return self
Validate that either credentials or client ID/secret are provided.
src/google/adk/tools/bigquery/bigquery_credentials.py