Return the authentication method AUTH_LOCAL.
Note that you need another authentication method that operates at
message level (like AUTH_NONE, AUTH_SYS, AUTH_DH), otherwise you will
get an error Auth_too_weak. AUTH_LOCAL overrides the result of the
other authentication method.
Return the pair (euid,egid) for a Unix domain socket.
The function raises Invalid_argument if it is not available for this
operating system. (Generally, this should work on Linux, BSD, and
Solaris, and OS with compatible system functions - supported methods are
SO_PEERCRED, getpeerucred, and getpeereid).
Some OS support this only for named Unix domain sockets but not for socketpairs.