Cookies

Cookies are key-value pairs stored on a web browser. They can be set (i.e. created) using client-side JavaScript. Conversely, a server can get a client's browser to set cookies via instructions in an HTTP response. As such, cookies can be set by both the client and the server.

Once a cookie is set, it is sent with every subsequent HTTP request addressed at the domain on which the cookie was set. Hence, if a cookie is set while using an application served on the domain example.com, it will not be sent to a server at otherdomain.com. However, cookies can be shared across subdomains. With the previous example, cookies will be sent to exampleapp.example.com.