def __init__(self, sar_client=None, wait_for_template_active_status=False, validate_only=False, parameters={}):
super(ServerlessAppPlugin, self).__init__(ServerlessAppPlugin.__name__)<EOL>self._applications = {}<EOL>self._in_progress_templates = []<EOL>self._sar_client = sar_client<EOL>self._wait_for_template_active_status = wait_for_template_active_status<EOL>self._validate_only = validate_only<EOL>self._parameters = parameters<EOL>if self._validate_only is True and self._wait_for_template_active_status is True:<EOL><INDENT>message = "<STR_LIT>"<EOL>raise InvalidPluginException(ServerlessAppPlugin.__name__, message)<EOL><DEDENT>
Initialize the plugin.

Explain that Validate_only uses a different API call, and does not produce a valid template.
:param boto3.client sar_client: The boto3 client to use to access the Serverless Application Repository
:param bool wait_for_template_active_status: Flag to wait for all templates to become active
:param bool validate_only: Flag to only validate application access (uses get_application API instead)