IRCv3 SASL capability + PLAIN method

Only plain, no other methods. We don't have built-in SSL to implement
EXTERNAL (certfp) and nothing else is worth implementing.

The actual authentication is pretty much like sending a server password
(when the server's authmode isn't closed), which means it happens in
cmd_identify, but this code also calls storage_check_pass() to send the
required success/failure replies.

SASL doesn't give us much benefit other than standards compliance, but
some clients might appreciate it.

And having a fifth way to do the same thing doesn't hurt! Now we have:

- identify in &bitlbee
- identify to nickserv (alias for root)
- 'nickserv' and 'ns' irc commands
- server password
- sasl plain

4 files changed, 143 insertions, 0 deletions

diff --git a/irc.h b/irc.h
index 4be7ce7e..f2df3b2e 100644
--- a/irc.h
+++ b/irc.h
@@ -49,6 +49,7 @@ typedef enum {
 	USTATUS_SHUTDOWN = 8,   /* Now used to indicate we're shutting down.
 	                           Currently just blocks irc_vawrite(). */
 	USTATUS_CAP_PENDING = 16,
+	USTATUS_SASL_PLAIN_PENDING = 32,
 
 	/* Not really status stuff, but other kinds of flags: For slightly
 	   better password security, since the only way to send passwords
@@ -66,6 +67,7 @@ typedef enum {
 } irc_status_t;
 
 typedef enum {
+	CAP_SASL = (1 << 0),
 	CAP_MULTI_PREFIX = (1 << 1),
 } irc_cap_flag_t;
 
diff --git a/irc_cap.c b/irc_cap.c
index 79732409..4cfc158b 100644
--- a/irc_cap.c
+++ b/irc_cap.c
@@ -37,6 +37,7 @@ typedef struct {
 } cap_info_t;
 
 static const cap_info_t supported_caps[] = {
+	{"sasl", CAP_SASL},
 	{"multi-prefix", CAP_MULTI_PREFIX},
 	{NULL},
 };
@@ -169,6 +170,12 @@ void irc_cmd_cap(irc_t *irc, char **cmd)
 
 	} else if (g_strcasecmp(cmd[1], "END") == 0) {
 		irc->status &= ~USTATUS_CAP_PENDING;
+
+		if (irc->status & USTATUS_SASL_PLAIN_PENDING) {
+			irc_send_num(irc, 906, ":SASL authentication aborted");
+			irc->status &= ~USTATUS_SASL_PLAIN_PENDING;
+		}
+
 		irc_check_login(irc);
 
 	} else {
diff --git a/irc_commands.c b/irc_commands.c
index 14a3fd9d..aa0ecb73 100644
--- a/irc_commands.c
+++ b/irc_commands.c
@@ -27,6 +27,7 @@
 #include "bitlbee.h"
 #include "help.h"
 #include "ipc.h"
+#include "base64.h"
 
 static void irc_cmd_pass(irc_t *irc, char **cmd)
 {
@@ -57,6 +58,120 @@ static void irc_cmd_pass(irc_t *irc, char **cmd)
 	}
 }
 
+static gboolean irc_sasl_plain_parse(char *input, char **user, char **pass)
+{
+	int i, part, len;
+	guint8 *decoded;
+	char *parts[2];
+
+	/* bitlbee's base64_decode wrapper adds an extra null terminator at the end */
+	len = base64_decode(input, &decoded);
+
+	/* this loop splits the decoded string into the parts array, like this:
+	   "username\0username\0password" -> {"username", "username", "password"} */
+
+	for (i = 0, part = 0; i < len && part < 3; part++) {
+		/* set each of parts[] to point to the beginning of a string */
+		parts[part] = (char *) decoded + i;
+
+		/* move the cursor forward to the next null terminator*/
+		i += strlen(parts[part]) + 1;
+	}
+
+	/* sanity checks */
+	if (part != 3 || i != (len + 1) || strcmp(parts[0], parts[1]) != 0) {
+		g_free(decoded);
+		return FALSE;
+	} else {
+		*user = g_strdup(parts[0]);
+		*pass = g_strdup(parts[2]);
+		g_free(decoded);
+		return TRUE;
+	}
+}
+
+static gboolean irc_sasl_check_pass(irc_t *irc, char *user, char *pass)
+{
+	storage_status_t status;
+
+	/* just check the password here to be able to reply with useful numerics
+	 * the actual identification will be handled later */
+	status = storage_check_pass(user, pass);
+
+	if (status == STORAGE_OK) {
+		if (!irc->user->nick) {
+			/* set the nick here so we have it for the following numeric */
+			irc->user->nick = g_strdup(user);
+		}
+		irc_send_num(irc, 903, ":Password accepted");
+		return TRUE;
+
+	} else if (status == STORAGE_INVALID_PASSWORD) {
+		irc_send_num(irc, 904, ":Incorrect password");
+	} else if (status == STORAGE_NO_SUCH_USER) {
+		irc_send_num(irc, 904, ":The nick is (probably) not registered");
+	} else {
+		irc_send_num(irc, 904, ":Unknown SASL authentication error");
+	}
+
+	return FALSE;
+}
+
+static void irc_cmd_authenticate(irc_t *irc, char **cmd)
+{
+	/* require the CAP to be enabled, and don't allow authentication before server password */
+	if (!(irc->caps & CAP_SASL) ||
+	    (global.conf->authmode == AUTHMODE_CLOSED && !(irc->status & USTATUS_AUTHORIZED))) {
+		return;
+	}
+
+	if (irc->status & USTATUS_SASL_PLAIN_PENDING) {
+		char *user, *pass;
+
+		irc->status &= ~USTATUS_SASL_PLAIN_PENDING;
+
+		if (!irc_sasl_plain_parse(cmd[1], &user, &pass)) {
+			irc_send_num(irc, 904, ":SASL authentication failed");
+			return;
+		}
+
+		/* let's not support the nick != user case
+		 * if NICK is received after SASL, it will just fail after registration */
+		if (user && irc->user->nick && strcmp(user, irc->user->nick) != 0) {
+			irc_send_num(irc, 902, ":Your SASL username does not match your nickname");
+
+		} else if (irc_sasl_check_pass(irc, user, pass)) {
+			/* and here we do the same thing as the PASS command*/
+			if (irc->status & USTATUS_LOGGED_IN) {
+				char *send_cmd[] = { "identify", pass, NULL };
+				root_command(irc, send_cmd);
+			} else {
+				/* no check_login here - wait for CAP END */
+				irc_setpass(irc, pass);
+			}
+		}
+
+		g_free(user);
+		g_free(pass);
+
+	} else if (irc->status & USTATUS_IDENTIFIED) {
+		irc_send_num(irc, 907, ":You have already authenticated");
+
+	} else if (strcmp(cmd[1], "*") == 0) {
+		irc_send_num(irc, 906, ":SASL authentication aborted");
+		irc->status &= ~USTATUS_SASL_PLAIN_PENDING;
+
+	} else if (g_strcasecmp(cmd[1], "PLAIN") == 0) {
+		irc_write(irc, "AUTHENTICATE +");
+		irc->status |= USTATUS_SASL_PLAIN_PENDING;
+
+	} else {
+		irc_send_num(irc, 908, "PLAIN :is the available SASL mechanism");
+		irc_send_num(irc, 904, ":SASL authentication failed");
+		irc->status &= ~USTATUS_SASL_PLAIN_PENDING;
+	}
+}
+
 static void irc_cmd_user(irc_t *irc, char **cmd)
 {
 	irc->user->user = g_strdup(cmd[1]);
@@ -82,6 +197,12 @@ static void irc_cmd_nick(irc_t *irc, char **cmd)
 			irc_setpass(irc, NULL);
 			irc->status &= ~USTATUS_IDENTIFIED;
 			irc_umode_set(irc, "-R", 1);
+
+			if (irc->caps & CAP_SASL) {
+				irc_send_num(irc, 901, "%s!%s@%s :You are now logged out",
+					irc->user->nick, irc->user->user, irc->user->host);
+			}
+
 			irc_rootmsg(irc, "Changing nicks resets your identify status. "
 			            "Re-identify or register a new account if you want "
 			            "your configuration to be saved. See \x02help "
@@ -721,6 +842,7 @@ static const command_t irc_commands[] = {
 	{ "rehash",      0, irc_cmd_rehash,      IRC_CMD_OPER_ONLY },
 	{ "restart",     0, NULL,                IRC_CMD_OPER_ONLY | IRC_CMD_TO_MASTER },
 	{ "kill",        2, NULL,                IRC_CMD_OPER_ONLY | IRC_CMD_TO_MASTER },
+	{ "authenticate", 1, irc_cmd_authenticate, 0 },
 	{ NULL }
 };
 
diff --git a/root_commands.c b/root_commands.c
index 7e1dc2a7..b5d0aef1 100644
--- a/root_commands.c
+++ b/root_commands.c
@@ -162,6 +162,12 @@ static void cmd_identify(irc_t *irc, char **cmd)
 		irc->status |= USTATUS_IDENTIFIED;
 		irc_umode_set(irc, "+R", 1);
 
+		if (irc->caps & CAP_SASL) {
+			irc_user_t *iu = irc->user;
+			irc_send_num(irc, 900, "%s!%s@%s %s :You are now logged in as %s",
+				iu->nick, iu->user, iu->host, iu->nick, iu->nick);
+		}
+
 		bitlbee_whatsnew(irc);
 
 		/* The following code is a bit hairy now. With takeover
@@ -238,6 +244,12 @@ static void cmd_register(irc_t *irc, char **cmd)
 		irc->status |= USTATUS_IDENTIFIED;
 		irc_umode_set(irc, "+R", 1);
 
+		if (irc->caps & CAP_SASL) {
+			irc_user_t *iu = irc->user;
+			irc_send_num(irc, 900, "%s!%s@%s %s :You are now logged in as %s",
+				iu->nick, iu->user, iu->host, iu->nick, iu->nick);
+		}
+
 		/* Set this var now, or anyone who logs in to his/her
 		   newly created account for the first time gets the
 		   whatsnew story. */