Explanation:
The JSON object for an AWS Config event contains a ruleParameters attribute, which is a set of key/value pairs that the AWS Lambda function receiving the event processes as part of its evaluation logic. You define parameters when you use the AWS Config console to create a custom rule. You can also define parameters with the InputParameters attribute in the PutConfigRule AWS Config API request or the put- config-rule AWS CLI command. The JSON code for the parameters is contained within a string, so a function must parse the string with a JSON parser to be able to evaluate its contents
Reference: http://docs.aws.amazon.com/config/latest/developerguide/evaluate-config_develop-rules_example-events.html