I am building the web application using Python-Flask. I want to authenticate JupyterHub user via my own web application without showing the login page. On other word, on click of button in my application, the JupyterHub user should be authenticated in the backend of my application and then the user should be able to access the JupyterHub notebook directly.
a custom LoginHandler that reads a cookie or header set by your application would be the way to do that, as described in this related discussion.