Cookie-based Access
The cookie-based authorization methods are based on choosing a magic cookie (an arbitrary piece of data) and passing it to the server when it is started; every client that can prove having knowledge of this cookie is then authorized connection to the server.
These cookies are created by a separate program and stored in the file .Xauthority in the user's home directory, by default. As a result, every program run by the client on the local computer can access this file and therefore the cookie that is necessary for being authorized by the server. If the user wants to start an application from another computer on the network, the cookie has to be copied to that other computer. How the cookie is copied is a system-dependent issue: for example, on Unix-like platforms, scp can be used to copy the cookie.
The two systems using this method are MIT-MAGIC-COOKIE-1 and XDM-AUTHORIZATION-1. In the first method, the client simply sends the cookie when requested to authenticate. In the second method, a secret key is also stored in the .Xauthority file. The client creates a string by concatenating the current time, a transport-dependent identifier, and the cookie, encrypts the resulting string, and sends it to the server.
The xauth application is a utility for accessing the .Xauthority file.
Read more about this topic: X Window Authorization
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