diff --git a/pam/pam.c b/pam/pam.c
index 7892b57..7940cc6 100644
--- a/pam/pam.c
+++ b/pam/pam.c
@@ -1,11 +1,11 @@
 #include <security/pam_ext.h>
 #include <security/pam_modules.h>
 #include <security/pam_modutil.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-// debug
-#include <stdio.h>
-#include <syslog.h>
+#include <sys/wait.h>
+#include <unistd.h>
 
 #ifdef sun
 #define PAM_CONST
@@ -13,6 +13,7 @@
 #define PAM_CONST const
 #endif
 #define MAXBUF 1024
+
 // source from: github.com/google/google-authenticator-libpam
 static int converse(pam_handle_t *pamh, int nargs, PAM_CONST struct pam_message **message,
                     struct pam_response **response)
@@ -51,28 +52,33 @@ static char *request_pass(pam_handle_t *pamh, int echocode, PAM_CONST char *prom
   return ret;
 }
 
-int exec_cmd(pam_handle_t *pamh, char *cmd, char *arg, char *res)
+int exec_cmd(char *user_env, char *from_env, char *argv[])
+{
+  char *envp[] = {user_env, from_env, NULL};
+  pid_t pid = fork();
+  if (pid == -1) {
+    return PAM_AUTHINFO_UNAVAIL;
+  } else if (pid == 0) {
+    execve(argv[0], argv, envp);
+    exit(-1);
+  } else {
+    int status;
+    if (wait(&status) == -1) {
+      return PAM_AUTHINFO_UNAVAIL;
+    } else if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+      return PAM_SUCCESS;
+    }
+  }
+  return PAM_AUTHINFO_UNAVAIL;
+}
+
+int popen_cmd(char *user_env, char *from_env, char *cmd, char *arg, char *res)
 {
-  const char *user;
-  const void *void_from = NULL;
-  const char *from;
   FILE *fp;
   char *c;
-  char user_env[MAXBUF], host_env[MAXBUF];
   char buf[MAXBUF];
-  if (pam_get_user(pamh, &user, NULL) != PAM_SUCCESS || user == NULL || *user == '\0') {
-    return PAM_USER_UNKNOWN;
-  }
-  sprintf(user_env, "USER=%s", user);
   putenv(user_env);
-
-  if (pam_get_item(pamh, PAM_RHOST, &void_from) != PAM_SUCCESS) {
-    return PAM_ABORT;
-  }
-
-  from = void_from;
-  sprintf(host_env, "SSH_CONNECTION=%s", from);
-  putenv(host_env);
+  putenv(from_env);
 
   if (arg != NULL) {
     c = malloc(strlen(cmd) + strlen(arg) + 2);
@@ -106,9 +112,23 @@ int exec_cmd(pam_handle_t *pamh, char *cmd, char *arg, char *res)
 
 int pam_sm_authenticate(pam_handle_t *pamh, int flags, int argc, const char **argv)
 {
-  char buf[MAXBUF], res[MAXBUF];
-  int ret = exec_cmd(pamh, "/usr/bin/google-web-oauth", "-only-url", res);
+  char res[MAXBUF];
+  const char *user;
+  const char *from;
+  char user_env[MAXBUF], from_env[MAXBUF];
+
+  if (pam_get_user(pamh, &user, NULL) != PAM_SUCCESS || user == NULL || *user == '\0') {
+    return PAM_USER_UNKNOWN;
+  }
+
+  if (pam_get_item(pamh, PAM_RHOST, (void *)&from) != PAM_SUCCESS) {
+    return PAM_ABORT;
+  }
+
+  sprintf(user_env, "USER=%s", user);
+  sprintf(from_env, "SSH_CONNECTION=%s", from);
 
+  int ret = popen_cmd(user_env, from_env, "/usr/bin/google-web-oauth", "-only-url", res);
   if (ret != 0) {
     return PAM_AUTHINFO_UNAVAIL;
   }
@@ -119,9 +139,9 @@ int pam_sm_authenticate(pam_handle_t *pamh, int flags, int argc, const char **ar
     return PAM_AUTHINFO_UNAVAIL;
   }
 
-  sprintf(buf, "-code %s", code);
-  ret = exec_cmd(pamh, "/usr/bin/google-web-oauth", buf, res);
-  if (ret != 0) {
+  char *arg[] = {"/usr/bin/google-web-oauth", "-code", code, NULL};
+  ret = exec_cmd(user_env, from_env, arg);
+  if (ret != PAM_SUCCESS) {
     goto err;
   }