This example shows how to build a simple Google App Engine web application that communicates with Google Earth Engine and allows a user to change parameters of a classifier using a basic form and the Google Maps API. Upon successful deployment, you will see a webpage with a Google map that lets you draw a rectangle, select a number of training points to use and then plot three layers (MODIS lancover, Landsat and upscaled MODIS landcover based on the classifier).
To set the app up yourself, download the Earth Engine API repository from GitHub:
git clone https://github.com/google/earthengine-api.git
Navigate to the Interactive Classifier example code:
cd ./earthengine-api/demos/interactive-classifier
Then follow the instructions in the Developer Docs to deploy an EE-based App Engine app. For the credentials section, you'll need a Service Account, not an OAuth2 Client ID.