Send text from web-site to Arduino Leonardo and output as HID keystrokes

I would like to use Arduino Leonardo to emulate a keyboard. I know this part of the problem.

Then I want to send a text from a Web-site on the Ethernet board to the keyboard output of the Leonardo. I do not quite understand how to grab the text from the client and over to the keyboard output of the Leonardo.

I am helping people with disability with computer accessibility.

I would appreciate an answer.

Then I want to send a text from a Web-site on the Ethernet board

The code that is running on the Arduino-as-server is where?

I do not quite understand how to grab the text from the client

Then, how do you know what to send to the client? Or, do you send the same response no matter what the client asks for?

The web-server is on the Arduino ethernet shield, which is mounted on the Leonardo. I want to send a text from a text input from a client to the Arduino and then forward it thru the USB cable to a thin client box (running Citrix) using the HID keyboard driver.

Background:
The reason to do it via an Arduino is that the Citrix environment does only allow me to do user interactions via standard keyboard (HID driver) and mouse input.

The web-server is on the Arduino ethernet shield, which is mounted on the Leonardo.

I STILL can't see the code.