- djm@cvs.openbsd.org 2012/10/30 21:29:55

     [auth-rsa.c auth.c auth.h auth2-pubkey.c servconf.c servconf.h]
     [sshd.c sshd_config sshd_config.5]
     new sshd_config option AuthorizedKeysCommand to support fetching
     authorized_keys from a command in addition to (or instead of) from
     the filesystem. The command is run as the target server user unless
     another specified via a new AuthorizedKeysCommandUser option.

     patch originally by jchadima AT redhat.com, reworked by me; feedback
     and ok markus@

10 files changed, 308 insertions, 43 deletions

diff --git a/ChangeLog b/ChangeLog
index 3cd16e480..27ec898b8 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -3,6 +3,16 @@
    - markus@cvs.openbsd.org 2012/10/05 12:34:39
      [sftp.c]
      fix signed vs unsigned warning; feedback & ok: djm@
+   - djm@cvs.openbsd.org 2012/10/30 21:29:55
+     [auth-rsa.c auth.c auth.h auth2-pubkey.c servconf.c servconf.h]
+     [sshd.c sshd_config sshd_config.5]
+     new sshd_config option AuthorizedKeysCommand to support fetching
+     authorized_keys from a command in addition to (or instead of) from
+     the filesystem. The command is run as the target server user unless
+     another specified via a new AuthorizedKeysCommandUser option.
+     
+     patch originally by jchadima AT redhat.com, reworked by me; feedback
+     and ok markus@
 
 20121019
  - (tim) [buildpkg.sh.in] Double up on some backslashes so they end up in
diff --git a/auth-rsa.c b/auth-rsa.c
index 4ab46cd51..2c8a7cb35 100644
--- a/auth-rsa.c
+++ b/auth-rsa.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth-rsa.c,v 1.80 2011/05/23 03:30:07 djm Exp $ */
+/* $OpenBSD: auth-rsa.c,v 1.81 2012/10/30 21:29:54 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -276,6 +276,8 @@ auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
         temporarily_use_uid(pw);
 
         for (i = 0; !allowed && i < options.num_authkeys_files; i++) {
+                if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
+                        continue;
                 file = expand_authorized_keys(
                     options.authorized_keys_files[i], pw);
                 allowed = rsa_key_allowed_in_file(pw, file, client_n, rkey);
diff --git a/auth.c b/auth.c
index a8cffd5c1..b5e1eefa0 100644
--- a/auth.c
+++ b/auth.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.c,v 1.96 2012/05/13 01:42:32 dtucker Exp $ */
+/* $OpenBSD: auth.c,v 1.97 2012/10/30 21:29:54 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -409,41 +409,42 @@ check_key_in_hostfiles(struct passwd *pw, Key *key, const char *host,
         return host_status;
 }
 
-
 /*
- * Check a given file for security. This is defined as all components
+ * Check a given path for security. This is defined as all components
  * of the path to the file must be owned by either the owner of
  * of the file or root and no directories must be group or world writable.
  *
  * XXX Should any specific check be done for sym links ?
  *
- * Takes an open file descriptor, the file name, a uid and and
+ * Takes an the file name, its stat information (preferably from fstat() to
+ * avoid races), the uid of the expected owner, their home directory and an
  * error buffer plus max size as arguments.
  *
  * Returns 0 on success and -1 on failure
  */
-static int
-secure_filename(FILE *f, const char *file, struct passwd *pw,
-    char *err, size_t errlen)
+int
+auth_secure_path(const char *name, struct stat *stp, const char *pw_dir,
+    uid_t uid, char *err, size_t errlen)
 {
-        uid_t uid = pw->pw_uid;
         char buf[MAXPATHLEN], homedir[MAXPATHLEN];
         char *cp;
         int comparehome = 0;
         struct stat st;
 
-        if (realpath(file, buf) == NULL) {
-                snprintf(err, errlen, "realpath %s failed: %s", file,
+        if (realpath(name, buf) == NULL) {
+                snprintf(err, errlen, "realpath %s failed: %s", name,
                     strerror(errno));
                 return -1;
         }
-        if (realpath(pw->pw_dir, homedir) != NULL)
+        if (pw_dir != NULL && realpath(pw_dir, homedir) != NULL)
                 comparehome = 1;
 
-        /* check the open file to avoid races */
-        if (fstat(fileno(f), &st) < 0 ||
-            (st.st_uid != 0 && st.st_uid != uid) ||
-            (st.st_mode & 022) != 0) {
+        if (!S_ISREG(stp->st_mode)) {
+                snprintf(err, errlen, "%s is not a regular file", buf);
+                return -1;
+        }
+        if ((stp->st_uid != 0 && stp->st_uid != uid) ||
+            (stp->st_mode & 022) != 0) {
                 snprintf(err, errlen, "bad ownership or modes for file %s",
                     buf);
                 return -1;
@@ -479,6 +480,28 @@ secure_filename(FILE *f, const char *file, struct passwd *pw,
         return 0;
 }
 
+/*
+ * Version of secure_path() that accepts an open file descriptor to
+ * avoid races.
+ *
+ * Returns 0 on success and -1 on failure
+ */
+static int
+secure_filename(FILE *f, const char *file, struct passwd *pw,
+    char *err, size_t errlen)
+{
+        char buf[MAXPATHLEN];
+        struct stat st;
+
+        /* check the open file to avoid races */
+        if (fstat(fileno(f), &st) < 0) {
+                snprintf(err, errlen, "cannot stat file %s: %s",
+                    buf, strerror(errno));
+                return -1;
+        }
+        return auth_secure_path(file, &st, pw->pw_dir, pw->pw_uid, err, errlen);
+}
+
 static FILE *
 auth_openfile(const char *file, struct passwd *pw, int strict_modes,
     int log_missing, char *file_type)
diff --git a/auth.h b/auth.h
index 0d786c4d5..063404167 100644
--- a/auth.h
+++ b/auth.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth.h,v 1.69 2011/05/23 03:30:07 djm Exp $ */
+/* $OpenBSD: auth.h,v 1.70 2012/10/30 21:29:54 djm Exp $ */
 
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
@@ -120,6 +120,10 @@ int	 auth_rhosts_rsa_key_allowed(struct passwd *, char *, char *, Key *);
 int      hostbased_key_allowed(struct passwd *, const char *, char *, Key *);
 int      user_key_allowed(struct passwd *, Key *);
 
+struct stat;
+int      auth_secure_path(const char *, struct stat *, const char *, uid_t,
+    char *, size_t);
+
 #ifdef KRB5
 int     auth_krb5(Authctxt *authctxt, krb5_data *auth, char **client, krb5_data *);
 int     auth_krb5_tgt(Authctxt *authctxt, krb5_data *tgt);
diff --git a/auth2-pubkey.c b/auth2-pubkey.c
index 5bccb5d76..ec8f75d57 100644
--- a/auth2-pubkey.c
+++ b/auth2-pubkey.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: auth2-pubkey.c,v 1.30 2011/09/25 05:44:47 djm Exp $ */
+/* $OpenBSD: auth2-pubkey.c,v 1.31 2012/10/30 21:29:54 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
@@ -27,9 +27,13 @@
 
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
 
+#include <errno.h>
 #include <fcntl.h>
+#include <paths.h>
 #include <pwd.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
@@ -240,7 +244,7 @@ match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert)
                         if (strcmp(cp, cert->principals[i]) == 0) {
                                 debug3("matched principal \"%.100s\" "
                                     "from file \"%s\" on line %lu",
-                                    cert->principals[i], file, linenum);
+                                    cert->principals[i], file, linenum);
                                 if (auth_parse_options(pw, line_opts,
                                     file, linenum) != 1)
                                         continue;
@@ -253,31 +257,22 @@ match_principals_file(char *file, struct passwd *pw, struct KeyCert *cert)
         fclose(f);
         restore_uid();
         return 0;
-}       
+}
 
-/* return 1 if user allows given key */
+/*
+ * Checks whether key is allowed in authorized_keys-format file,
+ * returns 1 if the key is allowed or 0 otherwise.
+ */
 static int
-user_key_allowed2(struct passwd *pw, Key *key, char *file)
+check_authkeys_file(FILE *f, char *file, Key* key, struct passwd *pw)
 {
         char line[SSH_MAX_PUBKEY_BYTES];
         const char *reason;
         int found_key = 0;
-        FILE *f;
         u_long linenum = 0;
         Key *found;
         char *fp;
 
-        /* Temporarily use the user's uid. */
-        temporarily_use_uid(pw);
-
-        debug("trying public key file %s", file);
-        f = auth_openkeyfile(file, pw, options.strict_modes);
-
-        if (!f) {
-                restore_uid();
-                return 0;
-        }
-
         found_key = 0;
         found = key_new(key_is_cert(key) ? KEY_UNSPEC : key->type);
 
@@ -370,8 +365,6 @@ user_key_allowed2(struct passwd *pw, Key *key, char *file)
                         break;
                 }
         }
-        restore_uid();
-        fclose(f);
         key_free(found);
         if (!found_key)
                 debug2("key not found");
@@ -433,7 +426,172 @@ user_cert_trusted_ca(struct passwd *pw, Key *key)
         return ret;
 }
 
-/* check whether given key is in .ssh/authorized_keys* */
+/*
+ * Checks whether key is allowed in file.
+ * returns 1 if the key is allowed or 0 otherwise.
+ */
+static int
+user_key_allowed2(struct passwd *pw, Key *key, char *file)
+{
+        FILE *f;
+        int found_key = 0;
+
+        /* Temporarily use the user's uid. */
+        temporarily_use_uid(pw);
+
+        debug("trying public key file %s", file);
+        if ((f = auth_openkeyfile(file, pw, options.strict_modes)) != NULL) {
+                found_key = check_authkeys_file(f, file, key, pw);
+                fclose(f);
+        }
+
+        restore_uid();
+        return found_key;
+}
+
+/*
+ * Checks whether key is allowed in output of command.
+ * returns 1 if the key is allowed or 0 otherwise.
+ */
+static int
+user_key_command_allowed2(struct passwd *user_pw, Key *key)
+{
+        FILE *f;
+        int ok, found_key = 0;
+        struct passwd *pw;
+        struct stat st;
+        int status, devnull, p[2], i;
+        pid_t pid;
+        char errmsg[512];
+
+        if (options.authorized_keys_command == NULL ||
+            options.authorized_keys_command[0] != '/')
+                return 0;
+
+        /* If no user specified to run commands the default to target user */
+        if (options.authorized_keys_command_user == NULL)
+                pw = user_pw;
+        else {
+                pw = getpwnam(options.authorized_keys_command_user);
+                if (pw == NULL) {
+                        error("AuthorizedKeyCommandUser \"%s\" not found: %s",
+                            options.authorized_keys_command, strerror(errno));
+                        return 0;
+                }
+        }
+
+        temporarily_use_uid(pw);
+
+        if (stat(options.authorized_keys_command, &st) < 0) {
+                error("Could not stat AuthorizedKeysCommand \"%s\": %s",
+                    options.authorized_keys_command, strerror(errno));
+                goto out;
+        }
+        if (auth_secure_path(options.authorized_keys_command, &st, NULL, 0,
+            errmsg, sizeof(errmsg)) != 0) {
+                error("Unsafe AuthorizedKeysCommand: %s", errmsg);
+                goto out;
+        }
+
+        if (pipe(p) != 0) {
+                error("%s: pipe: %s", __func__, strerror(errno));
+                goto out;
+        }
+
+        debug3("Running AuthorizedKeysCommand: \"%s\" as \"%s\"",
+            options.authorized_keys_command, pw->pw_name);
+
+        /*
+         * Don't want to call this in the child, where it can fatal() and
+         * run cleanup_exit() code.
+         */
+        restore_uid();
+
+        switch ((pid = fork())) {
+        case -1: /* error */
+                error("%s: fork: %s", __func__, strerror(errno));
+                close(p[0]);
+                close(p[1]);
+                return 0;
+        case 0: /* child */
+                for (i = 0; i < NSIG; i++)
+                        signal(i, SIG_DFL);
+
+                /* Don't use permanently_set_uid() here to avoid fatal() */
+                if (setresgid(pw->pw_gid, pw->pw_gid, pw->pw_gid) != 0) {
+                        error("setresgid %u: %s", (u_int)pw->pw_gid,
+                            strerror(errno));
+                        _exit(1);
+                }
+                if (setresuid(pw->pw_uid, pw->pw_uid, pw->pw_uid) != 0) {
+                        error("setresuid %u: %s", (u_int)pw->pw_uid,
+                            strerror(errno));
+                        _exit(1);
+                }
+
+                close(p[0]);
+                if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
+                        error("%s: open %s: %s", __func__, _PATH_DEVNULL,
+                            strerror(errno));
+                        _exit(1);
+                }
+                if (dup2(devnull, STDIN_FILENO) == -1 ||
+                    dup2(p[1], STDOUT_FILENO) == -1 ||
+                    dup2(devnull, STDERR_FILENO) == -1) {
+                        error("%s: dup2: %s", __func__, strerror(errno));
+                        _exit(1);
+                }
+                closefrom(STDERR_FILENO + 1);
+
+                execl(options.authorized_keys_command,
+                    options.authorized_keys_command, pw->pw_name, NULL);
+
+                error("AuthorizedKeysCommand %s exec failed: %s",
+                    options.authorized_keys_command, strerror(errno));
+                _exit(127);
+        default: /* parent */
+                break;
+        }
+
+        temporarily_use_uid(pw);
+
+        close(p[1]);
+        if ((f = fdopen(p[0], "r")) == NULL) {
+                error("%s: fdopen: %s", __func__, strerror(errno));
+                close(p[0]);
+                /* Don't leave zombie child */
+                kill(pid, SIGTERM);
+                while (waitpid(pid, NULL, 0) == -1 && errno == EINTR)
+                        ;
+                goto out;
+        }
+        ok = check_authkeys_file(f, options.authorized_keys_command, key, pw);
+        fclose(f);
+
+        while (waitpid(pid, &status, 0) == -1) {
+                if (errno != EINTR) {
+                        error("%s: waitpid: %s", __func__, strerror(errno));
+                        goto out;
+                }
+        }
+        if (WIFSIGNALED(status)) {
+                error("AuthorizedKeysCommand %s exited on signal %d",
+                    options.authorized_keys_command, WTERMSIG(status));
+                goto out;
+        } else if (WEXITSTATUS(status) != 0) {
+                error("AuthorizedKeysCommand %s returned status %d",
+                    options.authorized_keys_command, WEXITSTATUS(status));
+                goto out;
+        }
+        found_key = ok;
+ out:
+        restore_uid();
+        return found_key;
+}
+
+/*
+ * Check whether key authenticates and authorises the user.
+ */
 int
 user_key_allowed(struct passwd *pw, Key *key)
 {
@@ -449,9 +607,17 @@ user_key_allowed(struct passwd *pw, Key *key)
         if (success)
                 return success;
 
+        success = user_key_command_allowed2(pw, key);
+        if (success > 0)
+                return success;
+
         for (i = 0; !success && i < options.num_authkeys_files; i++) {
+
+                if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
+                        continue;
                 file = expand_authorized_keys(
                     options.authorized_keys_files[i], pw);
+
                 success = user_key_allowed2(pw, key, file);
                 xfree(file);
         }
diff --git a/servconf.c b/servconf.c
index f4b7dd58b..8e69ea5ce 100644
--- a/servconf.c
+++ b/servconf.c
@@ -1,5 +1,5 @@
 
-/* $OpenBSD: servconf.c,v 1.230 2012/09/13 23:37:36 dtucker Exp $ */
+/* $OpenBSD: servconf.c,v 1.231 2012/10/30 21:29:54 djm Exp $ */
 /*
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
  *                    All rights reserved
@@ -135,6 +135,8 @@ initialize_server_options(ServerOptions *options)
         options->num_permitted_opens = -1;
         options->adm_forced_command = NULL;
         options->chroot_directory = NULL;
+        options->authorized_keys_command = NULL;
+        options->authorized_keys_command_user = NULL;
         options->zero_knowledge_password_authentication = -1;
         options->revoked_keys_file = NULL;
         options->trusted_user_ca_keys = NULL;
@@ -329,6 +331,7 @@ typedef enum {
         sZeroKnowledgePasswordAuthentication, sHostCertificate,
         sRevokedKeys, sTrustedUserCAKeys, sAuthorizedPrincipalsFile,
         sKexAlgorithms, sIPQoS, sVersionAddendum,
+        sAuthorizedKeysCommand, sAuthorizedKeysCommandUser,
         sDeprecated, sUnsupported
 } ServerOpCodes;
 
@@ -453,6 +456,8 @@ static struct {
         { "authorizedprincipalsfile", sAuthorizedPrincipalsFile, SSHCFG_ALL },
         { "kexalgorithms", sKexAlgorithms, SSHCFG_GLOBAL },
         { "ipqos", sIPQoS, SSHCFG_ALL },
+        { "authorizedkeyscommand", sAuthorizedKeysCommand, SSHCFG_ALL },
+        { "authorizedkeyscommanduser", sAuthorizedKeysCommandUser, SSHCFG_ALL },
         { "versionaddendum", sVersionAddendum, SSHCFG_GLOBAL },
         { NULL, sBadOption, 0 }
 };
@@ -1498,6 +1503,25 @@ process_server_config_line(ServerOptions *options, char *line,
                 }
                 return 0;
 
+        case sAuthorizedKeysCommand:
+                len = strspn(cp, WHITESPACE);
+                if (*activep && options->authorized_keys_command == NULL) {
+                        if (cp[len] != '/' && strcasecmp(cp + len, "none") != 0)
+                                fatal("%.200s line %d: AuthorizedKeysCommand "
+                                    "must be an absolute path",
+                                    filename, linenum);
+                        options->authorized_keys_command = xstrdup(cp + len);
+                }
+                return 0;
+
+        case sAuthorizedKeysCommandUser:
+                charptr = &options->authorized_keys_command_user;
+
+                arg = strdelim(&cp);
+                if (*activep && *charptr == NULL)
+                        *charptr = xstrdup(arg);
+                break;
+
         case sDeprecated:
                 logit("%s line %d: Deprecated option %s",
                     filename, linenum, arg);
@@ -1648,6 +1672,8 @@ copy_set_server_options(ServerOptions *dst, ServerOptions *src, int preauth)
         M_CP_INTOPT(hostbased_uses_name_from_packet_only);
         M_CP_INTOPT(kbd_interactive_authentication);
         M_CP_INTOPT(zero_knowledge_password_authentication);
+        M_CP_STROPT(authorized_keys_command);
+        M_CP_STROPT(authorized_keys_command_user);
         M_CP_INTOPT(permit_root_login);
         M_CP_INTOPT(permit_empty_passwd);
 
@@ -1908,6 +1934,8 @@ dump_config(ServerOptions *o)
         dump_cfg_string(sAuthorizedPrincipalsFile,
             o->authorized_principals_file);
         dump_cfg_string(sVersionAddendum, o->version_addendum);
+        dump_cfg_string(sAuthorizedKeysCommand, o->authorized_keys_command);
+        dump_cfg_string(sAuthorizedKeysCommandUser, o->authorized_keys_command_user);
 
         /* string arguments requiring a lookup */
         dump_cfg_string(sLogLevel, log_level_name(o->log_level));
diff --git a/servconf.h b/servconf.h
index 096d596d7..0064c9bc5 100644
--- a/servconf.h
+++ b/servconf.h
@@ -1,4 +1,4 @@
-/* $OpenBSD: servconf.h,v 1.103 2012/07/10 02:19:15 djm Exp $ */
+/* $OpenBSD: servconf.h,v 1.104 2012/10/30 21:29:55 djm Exp $ */
 
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
@@ -166,6 +166,8 @@ typedef struct {
         char   *revoked_keys_file;
         char   *trusted_user_ca_keys;
         char   *authorized_principals_file;
+        char   *authorized_keys_command;
+        char   *authorized_keys_command_user;
 
         char   *version_addendum;       /* Appended to SSH banner */
 }       ServerOptions;
diff --git a/sshd.c b/sshd.c
index 9aff5e8af..eff0290b0 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: sshd.c,v 1.393 2012/07/10 02:19:15 djm Exp $ */
+/* $OpenBSD: sshd.c,v 1.394 2012/10/30 21:29:55 djm Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -359,6 +359,15 @@ grace_alarm_handler(int sig)
         if (use_privsep && pmonitor != NULL && pmonitor->m_pid > 0)
                 kill(pmonitor->m_pid, SIGALRM);
 
+        /*
+         * Try to kill any processes that we have spawned, E.g. authorized
+         * keys command helpers.
+         */
+        if (getpgid(0) == getpid()) {
+                signal(SIGTERM, SIG_IGN);
+                killpg(0, SIGTERM);
+        }
+
         /* Log error and exit. */
         sigdie("Timeout before authentication for %s", get_remote_ipaddr());
 }
diff --git a/sshd_config b/sshd_config
index 9424ee2c6..3d35bef02 100644
--- a/sshd_config
+++ b/sshd_config
@@ -1,4 +1,4 @@
-#       $OpenBSD: sshd_config,v 1.87 2012/07/10 02:19:15 djm Exp $
+#       $OpenBSD: sshd_config,v 1.88 2012/10/30 21:29:55 djm Exp $
 
 # This is the sshd server system-wide configuration file.  See
 # sshd_config(5) for more information.
@@ -51,6 +51,9 @@ AuthorizedKeysFile	.ssh/authorized_keys
 
 #AuthorizedPrincipalsFile none
 
+#AuthorizedKeysCommand none
+#AuthorizedKeysCommandUser nobody
+
 # For this to work you will also need host keys in /etc/ssh/ssh_known_hosts
 #RhostsRSAAuthentication no
 # similar for protocol version 2
diff --git a/sshd_config.5 b/sshd_config.5
index 987558ae8..de8f0f825 100644
--- a/sshd_config.5
+++ b/sshd_config.5
@@ -33,8 +33,8 @@
 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.\" $OpenBSD: sshd_config.5,v 1.145 2012/10/04 13:21:50 markus Exp $
-.Dd $Mdocdate: October 4 2012 $
+.\" $OpenBSD: sshd_config.5,v 1.146 2012/10/30 21:29:55 djm Exp $
+.Dd $Mdocdate: October 30 2012 $
 .Dt SSHD_CONFIG 5
 .Os
 .Sh NAME
@@ -151,6 +151,22 @@ See
 in
 .Xr ssh_config 5
 for more information on patterns.
+.It Cm AuthorizedKeysCommand
+Specifies a program to be used for lookup of the user's public keys.
+The program will be invoked with a single argument of the username
+being authenticated, and should produce on standard output zero or
+more lines of authorized_keys output (see AUTHORIZED_KEYS in
+.Xr sshd 8 )
+If a key supplied by AuthorizedKeysCommand does not successfully authenticate
+and authorize the user then public key authentication continues using the usual
+.Cm AuthorizedKeysFile
+files.
+By default, no AuthorizedKeysCommand is run.
+.It Cm AuthorizedKeysCommandUser
+Specifies the user under whose account the AuthorizedKeysCommand is run.
+The default is the user being authenticated.
+It is recommended to use a dedicated user that has no other role on the host
+than running authorized keys commands.
 .It Cm AuthorizedKeysFile
 Specifies the file that contains the public keys that can be used
 for user authentication.
@@ -712,6 +728,8 @@ Available keywords are
 .Cm AllowTcpForwarding ,
 .Cm AllowUsers ,
 .Cm AuthorizedKeysFile ,
+.Cm AuthorizedKeysCommand ,
+.Cm AuthorizedKeysCommandUser ,
 .Cm AuthorizedPrincipalsFile ,
 .Cm Banner ,
 .Cm ChrootDirectory ,