/* Copyright (C) 2002 Timo Sirainen */

/* Digest-MD5 SASL authentication, see RFC-2831 */

#include "common.h"
#include "base64.h"
#include "buffer.h"
#include "hex-binary.h"
#include "md5.h"
#include "randgen.h"
#include "str.h"
#include "mech.h"
#include "passdb.h"

#include <stdlib.h>

/* Linear whitespace */
#define IS_LWS(c) ((c) == ' ' || (c) == '\t')

enum qop_option {
	QOP_AUTH	= 0x01,	/* authenticate */
	QOP_AUTH_INT	= 0x02, /* + integrity protection, not supported yet */
	QOP_AUTH_CONF	= 0x04, /* + encryption, not supported yet */

	QOP_COUNT	= 3
};

static const char *qop_names[] = { "auth", "auth-int", "auth-conf" };

struct digest_auth_request {
	struct auth_request auth_request;

	pool_t pool;
	unsigned int authenticated:1;

	/* requested: */
	char *nonce;
	enum qop_option qop;

	/* received: */
	char *realm; /* may be NULL */
	char *username;
	char *cnonce;
	char *nonce_count;
	char *qop_value;
	char *digest_uri; /* may be NULL */
	unsigned char response[32];
	unsigned long maxbuf;
	unsigned int nonce_found:1;

	/* final reply: */
	char *rspauth;
};

static string_t *get_digest_challenge(struct digest_auth_request *auth)
{
	buffer_t *buf;
	string_t *str;
	const char *const *tmp;
	unsigned char nonce[16];
	int i, first_qop;

	/*
	   realm="hostname" (multiple allowed)
	   nonce="randomized data, at least 64bit"
	   qop="auth,auth-int,auth-conf"
	   maxbuf=number (with auth-int, auth-conf, defaults to 64k)
	   charset="utf-8" (iso-8859-1 if it doesn't exist)
	   algorithm="md5-sess"
	   cipher="3des,des,rc4-40,rc4,rc4-56" (with auth-conf)
	*/

	/* get 128bit of random data as nonce */
	random_fill(nonce, sizeof(nonce));

	t_push();
	buf = buffer_create_static(pool_datastack_create(),
				   MAX_BASE64_ENCODED_SIZE(sizeof(nonce))+1);

	base64_encode(nonce, sizeof(nonce), buf);
	buffer_append_c(buf, '\0');
	auth->nonce = p_strdup(auth->pool, buffer_get_data(buf, NULL));
	t_pop();

	str = t_str_new(256);

	for (tmp = auth_realms; *tmp != NULL; tmp++) {
		str_printfa(str, "realm=\"%s\"", *tmp);
		str_append_c(str, ',');
	}

	str_printfa(str, "nonce=\"%s\",", auth->nonce);

	str_append(str, "qop=\""); first_qop = TRUE;
	for (i = 0; i < QOP_COUNT; i++) {
		if (auth->qop & (1 << i)) {
			if (first_qop)
				first_qop = FALSE;
			else
				str_append_c(str, ',');
			str_append(str, qop_names[i]);
		}
	}
	str_append(str, "\",");

	str_append(str, "charset=\"utf-8\","
		   "algorithm=\"md5-sess\"");
	return str;
}

static int verify_credentials(struct digest_auth_request *auth,
			      const char *credentials)
{
	struct md5_context ctx;
	unsigned char digest[16];
	const char *a1_hex, *a2_hex, *response_hex;
	buffer_t *digest_buf;
	int i;

	/* get the MD5 password */
	if (credentials == NULL || strlen(credentials) != sizeof(digest)*2)
		return FALSE;

	digest_buf = buffer_create_data(pool_datastack_create(),
					digest, sizeof(digest));
	if (hex_to_binary(credentials, digest_buf) <= 0)
		return FALSE;

	/*
	   response =
	     HEX( KD ( HEX(H(A1)),
		     { nonce-value, ":" nc-value, ":",
		       cnonce-value, ":", qop-value, ":", HEX(H(A2)) }))

	   and since we don't support authzid yet:

	   A1 = { H( { username-value, ":", realm-value, ":", passwd } ),
		":", nonce-value, ":", cnonce-value }

	   If the "qop" directive's value is "auth", then A2 is:
	
	      A2       = { "AUTHENTICATE:", digest-uri-value }
	
	   If the "qop" value is "auth-int" or "auth-conf" then A2 is:
	
	      A2       = { "AUTHENTICATE:", digest-uri-value,
		       ":00000000000000000000000000000000" }
	*/

	/* A1 */
	md5_init(&ctx);
	md5_update(&ctx, digest, 16);
	md5_update(&ctx, ":", 1);
	md5_update(&ctx, auth->nonce, strlen(auth->nonce));
	md5_update(&ctx, ":", 1);
	md5_update(&ctx, auth->cnonce, strlen(auth->cnonce));
	md5_final(&ctx, digest);
	a1_hex = binary_to_hex(digest, 16);

	/* do it twice, first verify the user's response, the second is
	   sent for client as a reply */
	for (i = 0; i < 2; i++) {
		/* A2 */
		md5_init(&ctx);
		if (i == 0)
			md5_update(&ctx, "AUTHENTICATE:", 13);
		else
			md5_update(&ctx, ":", 1);

		if (auth->digest_uri != NULL) {
			md5_update(&ctx, auth->digest_uri,
				   strlen(auth->digest_uri));
		}
		if (auth->qop == QOP_AUTH_INT || auth->qop == QOP_AUTH_CONF) {
			md5_update(&ctx, ":00000000000000000000000000000000",
				   33);
		}
		md5_final(&ctx, digest);
		a2_hex = binary_to_hex(digest, 16);

		/* response */
		md5_init(&ctx);
		md5_update(&ctx, a1_hex, 32);
		md5_update(&ctx, ":", 1);
		md5_update(&ctx, auth->nonce, strlen(auth->nonce));
		md5_update(&ctx, ":", 1);
		md5_update(&ctx, auth->nonce_count, strlen(auth->nonce_count));
		md5_update(&ctx, ":", 1);
		md5_update(&ctx, auth->cnonce, strlen(auth->cnonce));
		md5_update(&ctx, ":", 1);
		md5_update(&ctx, auth->qop_value, strlen(auth->qop_value));
		md5_update(&ctx, ":", 1);
		md5_update(&ctx, a2_hex, 32);
		md5_final(&ctx, digest);
		response_hex = binary_to_hex(digest, 16);

		if (i == 0) {
			/* verify response */
			if (memcmp(response_hex, auth->response, 32) != 0) {
				if (verbose) {
					struct auth_request *auth_request =
						&auth->auth_request;
					i_info("digest-md5(%s): "
					       "password mismatch",
					       get_log_prefix(auth_request));
				}
				return FALSE;
			}
		} else {
			auth->rspauth = p_strconcat(auth->pool, "rspauth=",
						    response_hex, NULL);
		}
	}

	return TRUE;
}

static int verify_realm(const char *realm)
{
	const char *const *tmp;

	if (*realm == '\0')
		return TRUE;

	for (tmp = auth_realms; *tmp != NULL; tmp++) {
		if (strcasecmp(realm, *tmp) == 0)
			return TRUE;
	}

	return FALSE;
}

static int parse_next(char **data, char **key, char **value)
{
	/* @UNSAFE */
	char *p, *dest;

	p = *data;
	while (IS_LWS(*p)) p++;

	/* get key */
	*key = p;
	while (*p != '\0' && *p != '=' && *p != ',')
		p++;

	if (*p != '=') {
		*data = p;
		return FALSE;
	}

	*value = p+1;

	/* skip trailing whitespace in key */
	while (IS_LWS(p[-1]))
		p--;
	*p = '\0';

	/* get value */
	p = *value;
	while (IS_LWS(*p)) p++;

	if (*p != '"') {
		while (*p != '\0' && *p != ',')
			p++;

		*data = p+1;
		while (IS_LWS(p[-1]))
			p--;
		*p = '\0';
	} else {
		/* quoted string */
		*value = dest = ++p;
		while (*p != '\0' && *p != '"') {
			if (*p == '\\' && p[1] != '\0')
				p++;
			*dest++ = *p++;
		}

		*data = *p == '"' ? p+1 : p;
		*dest = '\0';
	}

	return TRUE;
}

static int auth_handle_response(struct digest_auth_request *auth,
				char *key, char *value, const char **error)
{
	int i;

	str_lcase(key);

	if (strcmp(key, "realm") == 0) {
		if (!verify_realm(value)) {
			*error = "Invalid realm";
			return FALSE;
		}
		if (auth->realm == NULL && *value != '\0')
			auth->realm = p_strdup(auth->pool, value);
		return TRUE;
	}

	if (strcmp(key, "username") == 0) {
		if (auth->username != NULL) {
			*error = "username must not exist more than once";
			return FALSE;
		}

		if (*value == '\0') {
			*error = "empty username";
			return FALSE;
		}

		auth->username = p_strdup(auth->pool, value);
		return TRUE;
	}

	if (strcmp(key, "nonce") == 0) {
		/* nonce must be same */
		if (strcmp(value, auth->nonce) != 0) {
			*error = "Invalid nonce";
			return FALSE;
		}

		auth->nonce_found = TRUE;
		return TRUE;
	}

	if (strcmp(key, "cnonce") == 0) {
		if (auth->cnonce != NULL) {
			*error = "cnonce must not exist more than once";
			return FALSE;
		}

		if (*value == '\0') {
			*error = "cnonce can't contain empty value";
			return FALSE;
		}

		auth->cnonce = p_strdup(auth->pool, value);
		return TRUE;
	}

	if (strcmp(key, "nonce-count") == 0) {
		if (auth->nonce_count != NULL) {
			*error = "nonce-count must not exist more than once";
			return FALSE;
		}

		if (atoi(value) != 1) {
			*error = "re-auth not supported currently";
			return FALSE;
		}

		auth->nonce_count = p_strdup(auth->pool, value);
		return TRUE;
	}

	if (strcmp(key, "qop") == 0) {
		for (i = 0; i < QOP_COUNT; i++) {
			if (strcasecmp(qop_names[i], value) == 0)
				break;
		}

		if (i == QOP_COUNT) {
			*error = "Unknown QoP value";
			return FALSE;
		}

		auth->qop &= (1 << i);
		if (auth->qop == 0) {
			*error = "Nonallowed QoP requested";
			return FALSE;
		} 

		auth->qop_value = p_strdup(auth->pool, value);
		return TRUE;
	}

	if (strcmp(key, "digest-uri") == 0) {
		/* type / host / serv-name */
		const char *const *uri = t_strsplit(value, "/");

		if (uri[0] == NULL || uri[1] == NULL) {
			*error = "Invalid digest-uri";
			return FALSE;
		}

		/* FIXME: RFC recommends that we verify the host/serv-type.
		   But isn't the realm enough already? That'd be just extra
		   configuration.. Maybe optionally list valid hosts in
		   config file? */
		auth->digest_uri = p_strdup(auth->pool, value);
		return TRUE;
	}

	if (strcmp(key, "maxbuf") == 0) {
		if (auth->maxbuf != 0) {
			*error = "maxbuf must not exist more than once";
			return FALSE;
		}

		auth->maxbuf = strtoul(value, NULL, 10);
		if (auth->maxbuf == 0) {
			*error = "Invalid maxbuf value";
			return FALSE;
		}
		return TRUE;
	}

	if (strcmp(key, "charset") == 0) {
		if (strcasecmp(value, "utf-8") != 0) {
			*error = "Only utf-8 charset is allowed";
			return FALSE;
		}

		return TRUE;
	}

	if (strcmp(key, "response") == 0) {
		if (strlen(value) != 32) {
			*error = "Invalid response value";
			return FALSE;
		}

		memcpy(auth->response, value, 32);
		return TRUE;
	}

	if (strcmp(key, "cipher") == 0) {
		/* not supported, ignore */
		return TRUE;
	}

	if (strcmp(key, "authzid") == 0) {
		/* not supported, abort */
		return FALSE;
	}

	/* unknown key, ignore */
	return TRUE;
}

static int parse_digest_response(struct digest_auth_request *auth,
				 const unsigned char *data, size_t size,
				 const char **error)
{
	char *copy, *key, *value;
	int failed;

	/*
	   realm="realm"
	   username="username"
	   nonce="randomized data"
	   cnonce="??"
	   nc=00000001
	   qop="auth|auth-int|auth-conf"
	   digest-uri="serv-type/host[/serv-name]"
	   response=32 HEX digits
	   maxbuf=number (with auth-int, auth-conf, defaults to 64k)
	   charset="utf-8" (iso-8859-1 if it doesn't exist)
	   cipher="cipher-value"
	   authzid="authzid-value"
	*/

	t_push();

	*error = NULL;
	failed = FALSE;

	copy = t_strdup_noconst(t_strndup(data, size));
	while (*copy != '\0') {
		if (parse_next(&copy, &key, &value)) {
			if (!auth_handle_response(auth, key, value, error)) {
				failed = TRUE;
				break;
			}
		}

		if (*copy == ',')
			copy++;
	}

	if (!failed) {
		if (!auth->nonce_found) {
			*error = "Missing nonce parameter";
			failed = TRUE;
		} else if (auth->cnonce == NULL) {
			*error = "Missing cnonce parameter";
			failed = TRUE;
		} else if (auth->username == NULL) {
			*error = "Missing username parameter";
			failed = TRUE;
		}
	}

	if (auth->nonce_count == NULL)
		auth->nonce_count = p_strdup(auth->pool, "00000001");
	if (auth->qop_value == NULL)
		auth->qop_value = p_strdup(auth->pool, "auth");

	t_pop();

	return !failed;
}

static void credentials_callback(const char *result,
				 struct auth_request *request)
{
	struct digest_auth_request *auth =
		(struct digest_auth_request *) request;
	struct auth_client_request_reply reply;

	if (!verify_credentials(auth, result)) {
		mech_auth_finish(request, NULL, 0, FALSE);
		return;
	}

	mech_init_auth_client_reply(&reply);
	reply.id = request->id;
	reply.result = AUTH_CLIENT_RESULT_CONTINUE;
	reply.data_size = strlen(auth->rspauth);
	auth->authenticated = TRUE;

	request->callback(&reply, auth->rspauth, request->conn);
}

static int
mech_digest_md5_auth_continue(struct auth_request *auth_request,
			      const unsigned char *data, size_t data_size,
			      mech_callback_t *callback)
{
	struct digest_auth_request *auth =
		(struct digest_auth_request *)auth_request;
	struct auth_client_request_reply reply;
	const char *error, *realm;

	/* initialize reply */
	mech_init_auth_client_reply(&reply);
	reply.id = auth_request->id;

	if (auth->authenticated) {
		/* authentication is done, we were just waiting the last
		   word from client */
		mech_auth_finish(auth_request, NULL, 0, TRUE);
		return TRUE;
	}

	if (parse_digest_response(auth, data, data_size, &error)) {
		auth_request->callback = callback;

		realm = auth->realm != NULL ? auth->realm : default_realm;
		if (realm == NULL) {
			auth_request->user = p_strdup(auth_request->pool,
						      auth->username);
		} else {
			auth_request->user = p_strconcat(auth_request->pool,
							 auth->username, "@",
							 realm, NULL);
		}

		if (mech_fix_username(auth_request->user)) {
			passdb->lookup_credentials(&auth->auth_request,
						PASSDB_CREDENTIALS_DIGEST_MD5,
						credentials_callback);
			return TRUE;
		}

		error = "invalid username";
	}

	if (error == NULL)
                error = "Authentication failed";
	else if (verbose) {
		i_info("digest-md5(%s): %s",
		       get_log_prefix(auth_request), error);
	}

	/* failed */
	reply.result = AUTH_CLIENT_RESULT_FAILURE;
	reply.data_size = strlen(error)+1;
	callback(&reply, error, auth_request->conn);
	return FALSE;
}

static int
mech_digest_md5_auth_initial(struct auth_request *auth_request,
			     struct auth_client_request_new *request,
			     const unsigned char *data __attr_unused__,
			     mech_callback_t *callback)
{
	struct digest_auth_request *auth =
		(struct digest_auth_request *)auth_request;
	struct auth_client_request_reply reply;
	string_t *challenge;
	size_t data_size;

	if (AUTH_CLIENT_REQUEST_HAVE_INITIAL_RESPONSE(request)) {
		/* FIXME: support subsequent authentication? */
		data += request->initial_resp_idx;
		data_size = request->data_size - request->initial_resp_idx;

		return auth_request->auth_continue(auth_request, data,
						   data_size, callback);
	}

	/* initialize reply */
	mech_init_auth_client_reply(&reply);
	reply.id = request->id;
	reply.result = AUTH_CLIENT_RESULT_CONTINUE;

	/* send the initial challenge */
	reply.reply_idx = 0;
	challenge = get_digest_challenge(auth);
	reply.data_size = str_len(challenge);
	callback(&reply, str_data(challenge), auth_request->conn);
	return TRUE;
}

static void mech_digest_md5_auth_free(struct auth_request *auth_request)
{
	pool_unref(auth_request->pool);
}

static struct auth_request *
mech_digest_md5_auth_new(void)
{
	struct digest_auth_request *auth;
	pool_t pool;

	pool = pool_alloconly_create("digest_md5_auth_request", 2048);
	auth = p_new(pool, struct digest_auth_request, 1);
	auth->pool = pool;

	auth->auth_request.refcount = 1;
	auth->auth_request.pool = pool;
	auth->auth_request.auth_initial = mech_digest_md5_auth_initial;
	auth->auth_request.auth_continue = mech_digest_md5_auth_continue;
	auth->auth_request.auth_free = mech_digest_md5_auth_free;
	auth->qop = QOP_AUTH;
	return &auth->auth_request;
}

struct mech_module mech_digest_md5 = {
	"DIGEST-MD5",

	MEMBER(plaintext) FALSE,
	MEMBER(advertise) TRUE,

	MEMBER(passdb_need_plain) FALSE,
	MEMBER(passdb_need_credentials) TRUE,

	mech_digest_md5_auth_new
};