Taken from: https://groups.google.com/g/linux.debian.bugs.dist/c/mX4GpUJih4k.

--- a/configure.ac
+++ b/configure.ac
@@ -132,6 +132,16 @@ if test "$os_unix" = "yes"; then
 	AC_CHECK_FUNCS([getpeereid])
 	AC_CHECK_FUNCS([getpeerucred])
 	AC_CHECK_FUNCS([issetugid])
+	case "$host_os" in
+	kfreebsd*-gnu | gnu*)
+		have_getpeereid=no
+		AC_CHECK_LIB(bsd, getpeereid, have_getpeereid=yes)
+		if test "x$have_getpeereid" = "xyes"; then
+			AC_DEFINE([HAVE_GETPEEREID], [1], [have getpeereid])
+			AC_SEARCH_LIBS([getpeereid], [bsd])
+		fi
+	;;
+	esac
 
 	AC_CACHE_CHECK([for thread-local storage class],
 		[ac_cv_tls_keyword],

--- a/common/unix-peer.c
+++ b/common/unix-peer.c
@@ -47,6 +47,11 @@
 #  include <ucred.h>
 #endif
 
+#ifdef HAVE_GETPEEREID
+/* Declare getpeereid from /usr/include/bsd/unistd.h */
+extern int getpeereid(int s, uid_t *euid, gid_t *egid);
+#endif
+
 /* Returns the unix domain socket peer information.
  * Returns zero on success.
  */
@@ -73,7 +78,8 @@ p11_get_upeer_id (int cfd, uid_t *uid, u
 		*pid = cr.pid;
 
 #elif defined(HAVE_GETPEEREID)
-	/* *BSD/MacOSX */
+	/* *BSD/MacOSX/kFreeBSD/Hurd */
+
 	uid_t euid;
 	gid_t egid;
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<tr><td><span title='2022-11-17 22:27:39 +0100'>2022-11-17</span></td><td><a href='/guix/commit/gnu/machine?id=17b01d546306885ff3c07e7b6aaffb541a8b9043'>machine: ssh: Validate 'system' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-11-09 13:45:24 +0100'>2022-11-09</span></td><td><a href='/guix/commit/gnu/machine?id=8d7cb7f2a4d0b7ce49764e4ba24026762d640da7'>machine/digital-ocean: Pull operating system definition out of string.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
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<tr><td><span title='2022-11-09 13:45:24 +0100'>2022-11-09</span></td><td><a href='/guix/commit/gnu/machine?id=e8dcd008a0be8bd967efabab6960d19e5424d93e'>machine/digital-ocean: Use static-networking-service-type.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2022-11-09 13:45:24 +0100'>2022-11-09</span></td><td><a href='/guix/commit/gnu/machine?id=c8e41af7be47fdd3ae16765d5cf892582f5a407a'>machine/digital-ocean: Use nightly Guix.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
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<tr><td><span title='2022-09-26 23:29:35 +0200'>2022-09-26</span></td><td><a href='/guix/commit/gnu/machine?id=1033645e9d3899edd6b052b19e24c0a718b95e88'>machine: ssh: Parameterize '%current-system' early on.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-09-04 17:57:02 +0200'>2022-09-04</span></td><td><a href='/guix/commit/gnu/machine?id=a451a809d5537035cc8888cfde5349842a68e934'>Fix misspelling of GUIX_DIGITAL_OCEAN_TOKEN.</a><span class='msg-avail'>...</span></td><td>Matthew James Kraai</td></tr>
<tr><td><span title='2022-03-01 10:30:17 -0500'>2022-03-01</span></td><td><a href='/guix/commit/gnu/machine?id=0dc019e19a23fea614be5623360849ab9bc35e74'>initrd: Use non-hyphenated kernel command-line parameter names.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-01-16 23:56:55 +0100'>2022-01-16</span></td><td><a href='/guix/commit/gnu/machine?id=084b76a70a6b302529f3450e6d07f1d105a10f7d'>machine: ssh: Add 'safety-checks?' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2022-01-09 23:17:17 +0100'>2022-01-09</span></td><td><a href='/guix/commit/gnu/machine?id=7f20e59a13a6acc3331e04185b8f1ed2538dcd0a'>machine: ssh: Open a single SSH session per machine.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>