identitySource

The identity source for which authorization is requested. For a `TOKEN` or `COGNITO_USER_POOLS` authorizer, this is required and specifies the request header mapping expression for the custom header holding the authorization token submitted by the client. For example, if the token header name is `Auth`, the header mapping expression is `method.request.header.Auth`. For the `REQUEST` authorizer, this is required when authorization caching is enabled. The value is a comma-separated string of one or more mapping expressions of the specified request parameters. For example, if an `Auth` header, a `Name` query string parameter are defined as identity sources, this value is `method.request.header.Auth, method.request.querystring.Name`. These parameters will be used to derive the authorization caching key and to perform runtime validation of the `REQUEST` authorizer by verifying all of the identity-related request parameters are present, not null and non-empty. Only when this is true does the authorizer invoke the authorizer Lambda function, otherwise, it returns a 401 Unauthorized response without calling the Lambda function. The valid value is a string of comma-separated mapping expressions of the specified request parameters. When the authorization caching is not enabled, this property is optional.