text: """API key system checks."""
  
  from django.conf import settings
  from django.core.checks import Error, register
  
  
  def _get_deprecated_setting_error(source, target, id):
      return Error(
          "Setting {} has been deprecated in v0.3".format(source),
          hint="Use the {} setting instead.".format(target),
          obj=settings,
          id="rest_framework_api_key.{}".format(id),
      )
  
  
  @register()
  def check_header_settings_for_deprecation(app_configs, **kwargs):
      """Check header settings.
  
      API key header settings have been updated to use the DRF_API_KEY_*
      namespace in version 0.3.
      """
      errors = []
      if hasattr(settings, "API_TOKEN_HEADER"):
          errors.append(
              _get_deprecated_setting_error(
                  source="API_TOKEN_HEADER", target="DRF_API_KEY_TOKEN_HEADER", id="E001"
              )
          )
      if hasattr(settings, "API_SECRET_KEY_HEADER"):
          errors.append(
              _get_deprecated_setting_error(
                  source="API_SECRET_KEY_HEADER",
                  target="DRF_API_KEY_SECRET_KEY_HEADER",
                  id="E002",
              )
          )
      return errors
  