MDEV-6577 auth_socket.so does not build in kFreeBSD

if it has to be a mess of ifdefs, then mess of ifdefs it is

plugin/auth_socket/CMakeLists.txt

@@ -22,18 +22,49 @@ int main() {
   getsockopt(0, SOL_SOCKET, SO_PEERCRED, &cred, 0);
 }" HAVE_PEERCRED)
  
-IF (NOT HAVE_PEERCRED)
+IF (HAVE_PEERCRED)
-  # Hi, OpenBSD!
+  ADD_DEFINITIONS(-DHAVE_PEERCRED)
-  CHECK_CXX_SOURCE_COMPILES(
+  SET(ok 1)
-  "#include <sys/types.h>
+ELSE()
-  #include <sys/socket.h>
+
-  int main() {
+# Hi, OpenBSD!
+CHECK_CXX_SOURCE_COMPILES(
+"#include <sys/types.h>
+#include <sys/socket.h>
+int main() {
   struct sockpeercred cred;
   getsockopt(0, SOL_SOCKET, SO_PEERCRED, &cred, 0);
   }" HAVE_SOCKPEERCRED)
-  ADD_DEFINITIONS(-Ducred=sockpeercred)
+
+IF (HAVE_SOCKPEERCRED)
+  ADD_DEFINITIONS(-DHAVE_SOCKPEERCRED)
+  SET(ok 1)
+ELSE()
+
+# FreeBSD, is that you?
+CHECK_CXX_SOURCE_COMPILES(
+"#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <sys/ucred.h>
+int main() {
+  struct xucred cred;
+  getsockopt(0, 0, LOCAL_PEERCRED, &cred, 0);
+  }" HAVE_XUCRED)
+
+IF (HAVE_XUCRED)
+  ADD_DEFINITIONS(-DHAVE_XUCRED)
+  SET(ok 1)
+ELSE()
+
+# Who else? Anyone?
+# C'mon, show your creativity, be different! ifdef's are fun, aren't they?
+
+ENDIF()
+ENDIF()
 ENDIF()
 
-IF(HAVE_PEERCRED OR HAVE_SOCKPEERCRED)
+IF(ok)
   MYSQL_ADD_PLUGIN(auth_socket auth_socket.c MODULE_ONLY)
 ENDIF()
+

plugin/auth_socket/auth_socket.c

@@ -27,9 +27,29 @@
 #define _GNU_SOURCE 1 /* for struct ucred */
 
 #include <mysql/plugin_auth.h>
-#include <sys/socket.h>
-#include <pwd.h>
 #include <string.h>
+#include <pwd.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#ifdef HAVE_PEERCRED
+#define level SOL_SOCKET
+
+#elif defined HAVE_SOCKPEERCRED
+#define level SOL_SOCKET
+#define ucred socketpeercred
+
+#elif defined HAVE_XUCRED
+#include <sys/un.h>
+#include <sys/ucred.h>
+#define level 0
+#define SO_PEERCRED LOCAL_PEERCRED
+#define uid cr_uid
+#define ucred xucred
+
+#else
+#error impossible
+#endif
 
 /**
   perform the unix socket based authentication
@@ -63,7 +83,7 @@ static int socket_auth(MYSQL_PLUGIN_VIO *vio, MYSQL_SERVER_AUTH_INFO *info)
     return CR_ERROR;
 
   /* get the UID of the client process */
-  if (getsockopt(vio_info.socket, SOL_SOCKET, SO_PEERCRED, &cred, &cred_len))
+  if (getsockopt(vio_info.socket, level, SO_PEERCRED, &cred, &cred_len))
     return CR_ERROR;
 
   if (cred_len != sizeof(cred))