webapp is an alias for org.apache.nutch.webui.NutchUiServer
Nutch Webapp is currently not available in Nutch 1.X. There is however a Jira ticket for backporting the REST API from Nutch 2.X to Nutch 1.X
Invoking the webapp starts a NutchUiServer on port 8080. There is a Jira ticket available for making the port configurable. The WebApp interacts directly with the Nutch 2.X REST API for configuring and administering your Nutch crawler. In it's current form, this webapp is designed to provide Nutch administration and configuration. The webapp is not designed to be an end-to-end system or a search application (yet).
Webapp has an authentication support with Jira ticket for Authentication Support for Web GUI. Default username and password configurations are:
One can customise it at nutch-site.xml.
You may also find the documentation on the Nutch 2.X RESTAPI useful.