diff -up openssh-5.6p1/auth2-pubkey.c.akc openssh-5.6p1/auth2-pubkey.c

--- openssh-5.6p1/auth2-pubkey.c.akc	2010-09-03 15:24:51.000000000 +0200

+++ openssh-5.6p1/auth2-pubkey.c	2010-09-03 15:24:51.000000000 +0200

@@ -27,6 +27,7 @@

 #include <sys/types.h>

 #include <sys/stat.h>

+#include <sys/wait.h>

 #include <fcntl.h>

 #include <pwd.h>

@@ -264,27 +265,15 @@ match_principals_file(char *file, struct

 /* return 1 if user allows given key */

 static int

-user_key_allowed2(struct passwd *pw, Key *key, char *file)

+user_search_key_in_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);

@@ -377,8 +366,6 @@ user_key_allowed2(struct passwd *pw, Key

 			break;

 		}

 	}

-	restore_uid();

-	fclose(f);

 	key_free(found);

 	if (!found_key)

 		debug2("key not found");

@@ -440,13 +427,191 @@ user_cert_trusted_ca(struct passwd *pw, 

 	return ret;

 }

-/* check whether given key is in .ssh/authorized_keys* */

+/* return 1 if user allows given key */

+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);

+	f = auth_openkeyfile(file, pw, options.strict_modes);

+

+ 	if (f) {

+ 		found_key = user_search_key_in_file (f, file, key, pw);

+		fclose(f);

+	}

+

+	restore_uid();

+	return found_key;

+}

+

+#ifdef WITH_AUTHORIZED_KEYS_COMMAND

+

+#define WHITESPACE " \t\r\n"

+

+/* return 1 if user allows given key */

+static int

+user_key_via_command_allowed2(struct passwd *pw, Key *key)

+{

+	FILE *f;

+	int found_key = 0;

+	char *progname = NULL;

+	char *cp;

+	struct passwd *runas_pw;

+	struct stat st;

+	int childdescriptors[2], i;

+	pid_t pstat, pid, child;

+

+	if (options.authorized_keys_command == NULL || options.authorized_keys_command[0] != '/')

+		return -1;

+

+	/* get the run as identity from config */

+	runas_pw = (options.authorized_keys_command_runas == NULL)? pw

+	    : getpwnam (options.authorized_keys_command_runas);

+	if (!runas_pw) {

+		error("%s: getpwnam(\"%s\"): %s", __func__,

+		    options.authorized_keys_command_runas, strerror(errno));

+		return 0;

+	}

+

+	/* Temporarily use the specified uid. */

+	if (runas_pw->pw_uid != 0)

+		temporarily_use_uid(runas_pw);

+

+	progname = xstrdup(options.authorized_keys_command);

+

+	debug3("%s: checking program '%s'", __func__, progname);

+

+	if (stat (progname, &st) < 0) {

+		error("%s: stat(\"%s\"): %s", __func__,

+		    progname, strerror(errno));

+		goto go_away;

+	}

+

+	if (st.st_uid != 0 || (st.st_mode & 022) != 0) {

+		error("bad ownership or modes for AuthorizedKeysCommand \"%s\"",

+		    progname);

+		goto go_away;

+	}

+

+	if (!S_ISREG(st.st_mode)) {

+		error("AuthorizedKeysCommand \"%s\" is not a regular file",

+		    progname);

+		goto go_away;

+	}

+

+	/*

+	 * Descend the path, checking that each component is a

+	 * root-owned directory with strict permissions.

+	 */

+	do {

+		if ((cp = strrchr(progname, '/')) == NULL)

+			break;

+		else 

+			*cp = '\0';

+	

+		debug3("%s: checking component '%s'", __func__, (*progname == '\0' ? "/" : progname));

+

+		if (stat((*progname == '\0' ? "/" : progname), &st) != 0) {

+			error("%s: stat(\"%s\"): %s", __func__,

+			    progname, strerror(errno));

+			goto go_away;

+		}

+		if (st.st_uid != 0 || (st.st_mode & 022) != 0) {

+			error("bad ownership or modes for AuthorizedKeysCommand path component \"%s\"",

+			    progname);

+			goto go_away;

+		}

+		if (!S_ISDIR(st.st_mode)) {

+			error("AuthorizedKeysCommand path component \"%s\" is not a directory",

+			    progname);

+			goto go_away;

+		}

+	} while (1);

+

+	/* open the pipe and read the keys */

+	if (pipe(childdescriptors)) {

+		error("failed to pipe(2) for AuthorizedKeysCommand: %s",

+		    strerror(errno));

+		goto go_away;

+	}

+

+	child = fork();

+	if (child == -1) {

+		error("failed to fork(2) for AuthorizedKeysCommand: %s",

+		    strerror(errno));

+		goto go_away;

+	} else if (child == 0) {

+		/* we're in the child process here -- we should never return from this block. */

+		/* permanently drop privs in child process */

+		if (runas_pw->pw_uid != 0) {

+			restore_uid();

+			permanently_set_uid(runas_pw);

+	  	}

+

+		close(childdescriptors[0]);

+		/* put the write end of the pipe on stdout (FD 1) */

+		if (dup2(childdescriptors[1], 1) == -1) {

+			error("failed to dup2(2) from AuthorizedKeysCommand: %s",

+			    strerror(errno));

+			_exit(127);

+		}

+

+		debug3("about to execl() AuthorizedKeysCommand: \"%s\" \"%s\"", options.authorized_keys_command, pw->pw_name);

+		/* see session.c:child_close_fds() */

+		for (i = 3; i < 64; ++i) {

+			close(i);

+		}

+

+		execl(options.authorized_keys_command, options.authorized_keys_command, pw->pw_name, NULL);

+

+		/* if we got here, it didn't work */

+		error("failed to execl AuthorizedKeysCommand: %s", strerror(errno)); /* this won't work because we closed the fds above */

+		_exit(127);

+	}

+	

+	close(childdescriptors[1]);

+	f = fdopen(childdescriptors[0], "r");

+	if (!f) {

+		error("%s: could not buffer FDs from AuthorizedKeysCommand (\"%s\", \"r\"): %s", __func__,

+		    options.authorized_keys_command, strerror (errno));

+		goto go_away;

+	}

+

+	found_key = user_search_key_in_file (f, options.authorized_keys_command, key, pw);

+	fclose (f);

+	do {

+		pid = waitpid(child, &pstat, 0);

+	} while (pid == -1 && errno == EINTR);

+

+	/* what about the return value from the child process? */

+go_away:

+	if (progname)

+		xfree (progname);

+

+	if (runas_pw->pw_uid != 0)

+		restore_uid();

+	return found_key;

+}

+#endif

+

+/* check whether given key is in 

 int

 user_key_allowed(struct passwd *pw, Key *key)

 {

 	int success;

 	char *file;

+#ifdef WITH_AUTHORIZED_KEYS_COMMAND

+	success = user_key_via_command_allowed2(pw, key);

+	if (success > 0)

+		return success;

+#endif

+

 	if (auth_key_is_revoked(key))

 		return 0;

 	if (key_is_cert(key) && auth_key_is_revoked(key->cert->signature_key))

diff -up openssh-5.6p1/configure.ac.akc openssh-5.6p1/configure.ac

--- openssh-5.6p1/configure.ac.akc	2010-09-03 15:24:51.000000000 +0200

+++ openssh-5.6p1/configure.ac	2010-09-03 15:24:51.000000000 +0200

@@ -1346,6 +1346,18 @@ AC_ARG_WITH(audit,

 	esac ]

 )

+# Check whether user wants AuthorizedKeysCommand support

+AKC_MSG="no"

+AC_ARG_WITH(authorized-keys-command,

+	[  --with-authorized-keys-command      Enable AuthorizedKeysCommand support],

+	[

+		if test "x$withval" != "xno" ; then

+			AC_DEFINE([WITH_AUTHORIZED_KEYS_COMMAND], 1, [Enable AuthorizedKeysCommand support])

+			AKC_MSG="yes"

+		fi

+	]

+)

+

 dnl    Checks for library functions. Please keep in alphabetical order

 AC_CHECK_FUNCS( \

 	arc4random \

@@ -4209,6 +4221,7 @@ echo "               Linux audit support

 echo "                 Smartcard support: $SCARD_MSG"

 echo "                     S/KEY support: $SKEY_MSG"

 echo "              TCP Wrappers support: $TCPW_MSG"

+echo "     AuthorizedKeysCommand support: $AKC_MSG"

 echo "              MD5 password support: $MD5_MSG"

 echo "                   libedit support: $LIBEDIT_MSG"

 echo "  Solaris process contract support: $SPC_MSG"

diff -up openssh-5.6p1/servconf.c.akc openssh-5.6p1/servconf.c

--- openssh-5.6p1/servconf.c.akc	2010-09-03 15:24:50.000000000 +0200

+++ openssh-5.6p1/servconf.c	2010-09-03 15:24:51.000000000 +0200

@@ -129,6 +129,8 @@ initialize_server_options(ServerOptions 

 	options->num_permitted_opens = -1;

 	options->adm_forced_command = NULL;

 	options->chroot_directory = NULL;

+	options->authorized_keys_command = NULL;

+	options->authorized_keys_command_runas = NULL;

 	options->zero_knowledge_password_authentication = -1;

 	options->revoked_keys_file = NULL;

 	options->trusted_user_ca_keys = NULL;

@@ -316,6 +318,7 @@ typedef enum {

 	sUsePrivilegeSeparation, sAllowAgentForwarding,

 	sZeroKnowledgePasswordAuthentication, sHostCertificate,

 	sRevokedKeys, sTrustedUserCAKeys, sAuthorizedPrincipalsFile,

+	sAuthorizedKeysCommand, sAuthorizedKeysCommandRunAs,

 	sDeprecated, sUnsupported

 } ServerOpCodes;

@@ -439,6 +442,13 @@ static struct {

 	{ "revokedkeys", sRevokedKeys, SSHCFG_ALL },

 	{ "trustedusercakeys", sTrustedUserCAKeys, SSHCFG_ALL },

 	{ "authorizedprincipalsfile", sAuthorizedPrincipalsFile, SSHCFG_ALL },

+#ifdef WITH_AUTHORIZED_KEYS_COMMAND

+	{ "authorizedkeyscommand", sAuthorizedKeysCommand, SSHCFG_ALL },

+	{ "authorizedkeyscommandrunas", sAuthorizedKeysCommandRunAs, SSHCFG_ALL },

+#else

+	{ "authorizedkeyscommand", sUnsupported, SSHCFG_ALL },

+	{ "authorizedkeyscommandrunas", sUnsupported, SSHCFG_ALL },

+#endif

 	{ NULL, sBadOption, 0 }

 };

@@ -1360,6 +1370,20 @@ process_server_config_line(ServerOptions

 		charptr = &options->revoked_keys_file;

 		goto parse_filename;

+	case sAuthorizedKeysCommand:

+		len = strspn(cp, WHITESPACE);

+		if (*activep && options->authorized_keys_command == NULL)

+			options->authorized_keys_command = xstrdup(cp + len);

+		return 0;

+

+	case sAuthorizedKeysCommandRunAs:

+		charptr = &options->authorized_keys_command_runas;

+

+		arg = strdelim(&cp;;

+		if (*activep && *charptr == NULL)

+			*charptr = xstrdup(arg);

+		break;

+

 	case sDeprecated:

 		logit("%s line %d: Deprecated option %s",

 		    filename, linenum, arg);

@@ -1453,6 +1477,8 @@ copy_set_server_options(ServerOptions *d

 	M_CP_INTOPT(gss_authentication);

 	M_CP_INTOPT(rsa_authentication);

 	M_CP_INTOPT(pubkey_authentication);

+	M_CP_STROPT(authorized_keys_command);

+	M_CP_STROPT(authorized_keys_command_runas);

 	M_CP_INTOPT(kerberos_authentication);

 	M_CP_INTOPT(hostbased_authentication);

 	M_CP_INTOPT(hostbased_uses_name_from_packet_only);

@@ -1705,6 +1731,8 @@ dump_config(ServerOptions *o)

 	dump_cfg_string(sRevokedKeys, o->revoked_keys_file);

 	dump_cfg_string(sAuthorizedPrincipalsFile,

 	    o->authorized_principals_file);

+	dump_cfg_string(sAuthorizedKeysCommand, o->authorized_keys_command);

+	dump_cfg_string(sAuthorizedKeysCommandRunAs, o->authorized_keys_command_runas);

 	/* string arguments requiring a lookup */

 	dump_cfg_string(sLogLevel, log_level_name(o->log_level));

diff -up openssh-5.6p1/servconf.h.akc openssh-5.6p1/servconf.h

--- openssh-5.6p1/servconf.h.akc	2010-09-03 15:24:50.000000000 +0200

+++ openssh-5.6p1/servconf.h	2010-09-03 15:24:51.000000000 +0200

@@ -158,6 +158,8 @@ typedef struct {

 	char   *revoked_keys_file;

 	char   *trusted_user_ca_keys;

 	char   *authorized_principals_file;

+	char   *authorized_keys_command;

+	char   *authorized_keys_command_runas;

 }       ServerOptions;

 void	 initialize_server_options(ServerOptions *);

diff -up openssh-5.6p1/sshd_config.0.akc openssh-5.6p1/sshd_config.0

--- openssh-5.6p1/sshd_config.0.akc	2010-09-03 15:24:50.000000000 +0200

+++ openssh-5.6p1/sshd_config.0	2010-09-03 15:27:26.000000000 +0200

@@ -71,6 +71,23 @@ DESCRIPTION

              See PATTERNS in ssh_config(5) for more information on patterns.

+     AuthorizedKeysCommand

+

+             Specifies a program to be used for lookup of the user's

+	     public keys.  The program will be invoked with its first

+	     argument the name of the user being authorized, and should produce 

+	     on standard output AuthorizedKeys lines (see AUTHORIZED_KEYS 

+	     in sshd(8)).  By default (or when set to the empty string) there is no

+	     AuthorizedKeysCommand run.  If the AuthorizedKeysCommand does not successfully

+	     authorize the user, authorization falls through to the

+	     AuthorizedKeysFile.  Note that this option has an effect

+	     only with PubkeyAuthentication turned on.

+

+     AuthorizedKeysCommandRunAs

+             Specifies the user under whose account the AuthorizedKeysCommand is run.

+             Empty string (the default value) means the user being authorized

+             is used.

+

      AuthorizedKeysFile

              Specifies the file that contains the public keys that can be used

              for user authentication.  The format is described in the

@@ -375,7 +392,8 @@ DESCRIPTION

              Only a subset of keywords may be used on the lines following a

              Match keyword.  Available keywords are AllowAgentForwarding,

-             AllowTcpForwarding, AuthorizedKeysFile, AuthorizedPrincipalsFile,

+             AllowTcpForwarding, AuthorizedKeysFile, AuthorizedKeysCommand,

+             AuthorizedKeysCommandRunAs, AuthorizedPrincipalsFile,

              Banner, ChrootDirectory, ForceCommand, GatewayPorts,

              GSSAPIAuthentication, HostbasedAuthentication,

              HostbasedUsesNameFromPacketOnly, KbdInteractiveAuthentication,

diff -up openssh-5.6p1/sshd_config.5.akc openssh-5.6p1/sshd_config.5

--- openssh-5.6p1/sshd_config.5.akc	2010-09-03 15:24:50.000000000 +0200

+++ openssh-5.6p1/sshd_config.5	2010-09-03 15:24:51.000000000 +0200

@@ -654,6 +654,8 @@ Available keywords are

 .Cm AllowAgentForwarding ,

 .Cm AllowTcpForwarding ,

 .Cm AuthorizedKeysFile ,

+.Cm AuthorizedKeysCommand ,

+.Cm AuthorizedKeysCommandRunAs ,

 .Cm AuthorizedPrincipalsFile ,

 .Cm Banner ,

 .Cm ChrootDirectory ,

@@ -666,6 +668,7 @@ Available keywords are

 .Cm KerberosAuthentication ,

 .Cm MaxAuthTries ,

 .Cm MaxSessions ,

+.Cm PubkeyAuthentication ,

 .Cm PasswordAuthentication ,

 .Cm PermitEmptyPasswords ,

 .Cm PermitOpen ,

@@ -868,6 +871,20 @@ Specifies a list of revoked public keys.

 Keys listed in this file will be refused for public key authentication.

 Note that if this file is not readable, then public key authentication will

 be refused for all users.

+.It Cm AuthorizedKeysCommand

+Specifies a program to be used for lookup of the user's

+public keys.  The program will be invoked with its first

+argument the name of the user being authorized, and should produce 

+on standard output AuthorizedKeys lines (see AUTHORIZED_KEYS 

+in sshd(8)).  By default (or when set to the empty string) there is no

+AuthorizedKeysCommand run.  If the AuthorizedKeysCommand does not successfully

+authorize the user, authorization falls through to the

+AuthorizedKeysFile.  Note that this option has an effect

+only with PubkeyAuthentication turned on.

+.It Cm AuthorizedKeysCommandRunAs

+Specifies the user under whose account the AuthorizedKeysCommand is run. Empty

+string (the default value) means the user being authorized is used.

+.Dq 

 .It Cm RhostsRSAAuthentication

 Specifies whether rhosts or /etc/hosts.equiv authentication together

 with successful RSA host authentication is allowed.

diff -up openssh-5.6p1/sshd_config.akc openssh-5.6p1/sshd_config

--- openssh-5.6p1/sshd_config.akc	2010-09-03 15:24:50.000000000 +0200

+++ openssh-5.6p1/sshd_config	2010-09-03 15:24:51.000000000 +0200

@@ -45,6 +45,8 @@ SyslogFacility AUTHPRIV

 #RSAAuthentication yes

 #PubkeyAuthentication yes

 #AuthorizedKeysFile	.ssh/authorized_keys

+#AuthorizedKeysCommand none

+#AuthorizedKeysCommandRunAs nobody

 # For this to work you will also need host keys in /etc/ssh/ssh_known_hosts

 #RhostsRSAAuthentication no