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+pam_xauth — PAM module to forward xauth keys between users
+The pam_xauth PAM module is designed to forward xauth keys (sometimes referred
+to as "cookies") between users.
+Without pam_xauth, when xauth is enabled and a user uses the su(1) command to
+assume another user's priviledges, that user is no longer able to access the
+original user's X display because the new user does not have the key needed to
+access the display. pam_xauth solves the problem by forwarding the key from the
+user running su (the source user) to the user whose identity the source user is
+assuming (the target user) when the session is created, and destroying the key
+when the session is torn down.
+This means, for example, that when you run su(1) from an xterm sesssion, you
+will be able to run X programs without explicitly dealing with the xauth(1)
+xauth command or ~/.Xauthority files.
+pam_xauth will only forward keys if xauth can list a key connected to the
+$DISPLAY environment variable.
+Primitive access control is provided by ~/.xauth/export in the invoking user's
+home directory and ~/.xauth/import in the target user's home directory.
+If a user has a ~/.xauth/import file, the user will only receive cookies from
+users listed in the file. If there is no ~/.xauth/import file, the user will
+accept cookies from any other user.
+If a user has a .xauth/export file, the user will only forward cookies to users
+listed in the file. If there is no ~/.xauth/export file, and the invoking user
+is not root, the user will forward cookies to any other user. If there is no ~
+/.xauth/export file, and the invoking user is root, the user will not forward
+cookies to other users.
+Both the import and export files support wildcards (such as *). Both the import
+and export files can be empty, signifying that no users are allowed.
+ Print debug information.
+ Specify the path the xauth program (it is expected in /usr/X11R6/bin/xauth,
+ /usr/bin/xauth, or /usr/bin/X11/xauth by default).
+ Specify the highest UID which will be assumed to belong to a "system" user.
+ pam_xauth will refuse to forward credentials to users with UID less than or
+ equal to this number, except for root and the "targetuser", if specified.
+ Specify a single target UID which is exempt from the systemuser check.
+Add the following line to /etc/pam.d/su to forward xauth keys between users
+when calling su:
+session optional pam_xauth.so
+pam_xauth will work only if it is used from a setuid application in which the
+getuid() call returns the id of the user running the application, and for which
+PAM can supply the name of the account that the user is attempting to assume.
+The typical application of this type is su(1). The application must call both
+pam_open_session() and pam_close_session() with the ruid set to the uid of the
+calling user and the euid set to root, and must have provided as the PAM_USER
+item the name of the target user.
+pam_xauth calls xauth(1) as the source user to extract the key for $DISPLAY,
+then calls xauth as the target user to merge the key into the a temporary
+database and later remove the database.
+pam_xauth cannot be told to not remove the keys when the session is closed.
+pam_xauth was written by Nalin Dahyabhai <email@example.com>, based on original
+version by Michael K. Johnson <firstname.lastname@example.org>.