What are cookies and how are they used in HTTP protocol?

• Cookies are small text blocks that are being sent in a HTTP requests to the web server and in a HTTP response from the web server.
• Each cookie consists of key-value pair, list of all cookies is represented by the HTTP header.
• Cookie is usually created on the server (by the on-line application back-end)
• Cookie can be created on the client-side (by the browser)
• Cookies are persisted in the browser
• All cookies can be seen in Chrome DevTools

Cookie example

Cookie: _ga=GA1.2.329801189.1515987465; ai_user=Xabc|2018-02-11T23:24:12.252Z;