xref: /lighttpd1.4/src/mod_auth.c (revision 3dd3cde9)

#include "first.h"

#include "base.h"
#include "plugin.h"
#include "http_auth.h"
#include "http_header.h"
#include "log.h"

#include <stdlib.h>
#include <string.h>

/**
 * auth framework
 */

typedef struct {
	/* auth */
	array  *auth_require;
	buffer *auth_backend_conf;
	unsigned short auth_extern_authn;

	/* generated */
	const http_auth_backend_t *auth_backend;
} plugin_config;

typedef struct {
	PLUGIN_DATA;

	plugin_config **config_storage;

	plugin_config conf;
} plugin_data;

static handler_t mod_auth_check_basic(server *srv, connection *con, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend);
static handler_t mod_auth_check_digest(server *srv, connection *con, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend);
static handler_t mod_auth_check_extern(server *srv, connection *con, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend);

INIT_FUNC(mod_auth_init) {
	static const http_auth_scheme_t http_auth_scheme_basic  = { "basic",  mod_auth_check_basic,  NULL };
	static const http_auth_scheme_t http_auth_scheme_digest = { "digest", mod_auth_check_digest, NULL };
	static const http_auth_scheme_t http_auth_scheme_extern = { "extern", mod_auth_check_extern, NULL };
	plugin_data *p;

	/* register http_auth_scheme_* */
	http_auth_scheme_set(&http_auth_scheme_basic);
	http_auth_scheme_set(&http_auth_scheme_digest);
	http_auth_scheme_set(&http_auth_scheme_extern);

	p = calloc(1, sizeof(*p));

	return p;
}

FREE_FUNC(mod_auth_free) {
	plugin_data *p = p_d;

	UNUSED(srv);

	if (!p) return HANDLER_GO_ON;

	if (p->config_storage) {
		size_t i;
		for (i = 0; i < srv->config_context->used; i++) {
			plugin_config *s = p->config_storage[i];

			if (NULL == s) continue;

			array_free(s->auth_require);
			buffer_free(s->auth_backend_conf);

			free(s);
		}
		free(p->config_storage);
	}

	free(p);

	return HANDLER_GO_ON;
}

/* data type for mod_auth structured data
 * (parsed from auth.require array of strings) */
typedef struct {
    DATA_UNSET;
    http_auth_require_t *require;
} data_auth;

static void data_auth_free(data_unset *d)
{
    data_auth * const dauth = (data_auth *)d;
    buffer_free(dauth->key);
    http_auth_require_free(dauth->require);
    free(dauth);
}

static data_auth *data_auth_init(void)
{
    data_auth * const dauth = calloc(1, sizeof(*dauth));
    force_assert(NULL != dauth);
    dauth->copy       = NULL; /* must not be called on this data */
    dauth->free       = data_auth_free;
    dauth->reset      = NULL; /* must not be called on this data */
    dauth->insert_dup = NULL; /* must not be called on this data */
    dauth->print      = NULL; /* must not be called on this data */
    dauth->type       = TYPE_OTHER;

    dauth->key = buffer_init();
    dauth->require = http_auth_require_init();

    return dauth;
}

static int mod_auth_require_parse (server *srv, http_auth_require_t * const require, const buffer *b)
{
    /* user=name1|user=name2|group=name3|host=name4 */

    const char *str = b->ptr;
    const char *p;

    if (buffer_is_equal_string(b, CONST_STR_LEN("valid-user"))) {
        require->valid_user = 1;
        return 1; /* success */
    }

    do {
        const char *eq;
        size_t len;
        p = strchr(str, '|');
        len = NULL != p ? (size_t)(p - str) : strlen(str);
        eq = memchr(str, '=', len);
        if (NULL == eq) {
            log_error_write(srv, __FILE__, __LINE__, "sssbss",
                            "error parsing auth.require 'require' field: missing '='",
                            "(expecting \"valid-user\" or \"user=a|user=b|group=g|host=h\").",
                            "error value:", b, "error near:", str);
            return 0;
        }
        if (p-1  == eq) {
            log_error_write(srv, __FILE__, __LINE__, "sssbss",
                            "error parsing auth.require 'require' field: missing token after '='",
                            "(expecting \"valid-user\" or \"user=a|user=b|group=g|host=h\").",
                            "error value:", b, "error near:", str);
            return 0;
        }

        switch ((int)(eq - str)) {
          case 4:
            if (0 == memcmp(str, CONST_STR_LEN("user"))) {
                data_string *ds = data_string_init();
                buffer_copy_string_len(ds->key,str+5,len-5); /*("user=" is 5)*/
                array_insert_unique(require->user, (data_unset *)ds);
                continue;
            }
            else if (0 == memcmp(str, CONST_STR_LEN("host"))) {
                data_string *ds = data_string_init();
                buffer_copy_string_len(ds->key,str+5,len-5); /*("host=" is 5)*/
                array_insert_unique(require->host, (data_unset *)ds);
                log_error_write(srv, __FILE__, __LINE__, "ssb",
                                "warning parsing auth.require 'require' field: 'host' not implemented;",
                                "field value:", b);
                continue;
            }
            break; /* to error */
          case 5:
            if (0 == memcmp(str, CONST_STR_LEN("group"))) {
                data_string *ds = data_string_init();
                buffer_copy_string_len(ds->key,str+6,len-6); /*("group=" is 6)*/
                array_insert_unique(require->group, (data_unset *)ds);
              #if 0/*(supported by mod_authn_ldap, but not all other backends)*/
                log_error_write(srv, __FILE__, __LINE__, "ssb",
                                "warning parsing auth.require 'require' field: 'group' not implemented;",
                                "field value:", b);
              #endif
                continue;
            }
            break; /* to error */
          case 10:
            if (0 == memcmp(str, CONST_STR_LEN("valid-user"))) {
                log_error_write(srv, __FILE__, __LINE__, "sssb",
                                "error parsing auth.require 'require' field: valid user can not be combined with other require rules",
                                "(expecting \"valid-user\" or \"user=a|user=b|group=g|host=h\").",
                                "error value:", b);
                return 0;
            }
            break; /* to error */
          default:
            break; /* to error */
        }

        log_error_write(srv, __FILE__, __LINE__, "sssbss",
                        "error parsing auth.require 'require' field: invalid/unsupported token",
                        "(expecting \"valid-user\" or \"user=a|user=b|group=g|host=h\").",
                        "error value:", b, "error near:", str);
        return 0;

    } while (p && *((str = p+1)));

    return 1; /* success */
}

SETDEFAULTS_FUNC(mod_auth_set_defaults) {
	plugin_data *p = p_d;
	size_t i;

	config_values_t cv[] = {
		{ "auth.backend",                   NULL, T_CONFIG_STRING, T_CONFIG_SCOPE_CONNECTION }, /* 0 */
		{ "auth.require",                   NULL, T_CONFIG_LOCAL, T_CONFIG_SCOPE_CONNECTION },  /* 1 */
		{ "auth.extern-authn",              NULL, T_CONFIG_BOOLEAN, T_CONFIG_SCOPE_CONNECTION },/* 2 */
		{ NULL,                             NULL, T_CONFIG_UNSET, T_CONFIG_SCOPE_UNSET }
	};

	p->config_storage = calloc(1, srv->config_context->used * sizeof(plugin_config *));

	for (i = 0; i < srv->config_context->used; i++) {
		data_config const* config = (data_config const*)srv->config_context->data[i];
		plugin_config *s;
		size_t n;
		data_array *da;

		s = calloc(1, sizeof(plugin_config));
		s->auth_backend_conf = buffer_init();

		s->auth_require = array_init();

		cv[0].destination = s->auth_backend_conf;
		cv[1].destination = s->auth_require; /* T_CONFIG_LOCAL; not modified by config_insert_values_global() */
		cv[2].destination = &s->auth_extern_authn;

		p->config_storage[i] = s;

		if (0 != config_insert_values_global(srv, config->value, cv, i == 0 ? T_CONFIG_SCOPE_SERVER : T_CONFIG_SCOPE_CONNECTION)) {
			return HANDLER_ERROR;
		}

		if (!buffer_string_is_empty(s->auth_backend_conf)) {
			s->auth_backend = http_auth_backend_get(s->auth_backend_conf);
			if (NULL == s->auth_backend) {
				log_error_write(srv, __FILE__, __LINE__, "sb", "auth.backend not supported:", s->auth_backend_conf);

				return HANDLER_ERROR;
			}
		}

		/* no auth.require for this section */
		if (NULL == (da = (data_array *)array_get_element(config->value, "auth.require"))) continue;

		if (da->type != TYPE_ARRAY || !array_is_kvarray(da->value)) {
			log_error_write(srv, __FILE__, __LINE__, "ss",
					"unexpected value for auth.require; expected ",
					"auth.require = ( \"urlpath\" => ( \"option\" => \"value\" ) )");
			return HANDLER_ERROR;
		}


		for (n = 0; n < da->value->used; n++) {
			size_t m;
			data_array *da_file = (data_array *)da->value->data[n];
			const buffer *method = NULL, *realm = NULL, *require = NULL;
			const http_auth_scheme_t *auth_scheme;

			if (!array_is_kvstring(da_file->value)) {
				log_error_write(srv, __FILE__, __LINE__, "ss",
						"unexpected value for auth.require; expected ",
						"auth.require = ( \"urlpath\" => ( \"option\" => \"value\" ) )");

				return HANDLER_ERROR;
			}

			for (m = 0; m < da_file->value->used; m++) {
				if (da_file->value->data[m]->type == TYPE_STRING) {
					data_string *ds = (data_string *)da_file->value->data[m];
					if (buffer_is_equal_string(ds->key, CONST_STR_LEN("method"))) {
						method = ds->value;
					} else if (buffer_is_equal_string(ds->key, CONST_STR_LEN("realm"))) {
						realm = ds->value;
					} else if (buffer_is_equal_string(ds->key, CONST_STR_LEN("require"))) {
						require = ds->value;
					} else {
						log_error_write(srv, __FILE__, __LINE__, "ssbs",
							"the field is unknown in:",
							"auth.require = ( \"...\" => ( ..., -> \"",
							da_file->value->data[m]->key,
							"\" <- => \"...\" ) )");

						return HANDLER_ERROR;
					}
				} else {
					log_error_write(srv, __FILE__, __LINE__, "ssbs",
						"a string was expected for:",
						"auth.require = ( \"...\" => ( ..., -> \"",
						da_file->value->data[m]->key,
						"\" <- => \"...\" ) )");

					return HANDLER_ERROR;
				}
			}

			if (buffer_string_is_empty(method)) {
				log_error_write(srv, __FILE__, __LINE__, "ss",
						"the method field is missing or blank in:",
						"auth.require = ( \"...\" => ( ..., \"method\" => \"...\" ) )");
				return HANDLER_ERROR;
			} else {
				auth_scheme = http_auth_scheme_get(method);
				if (NULL == auth_scheme) {
					log_error_write(srv, __FILE__, __LINE__, "sbss",
							"unknown method", method, "(e.g. \"basic\", \"digest\" or \"extern\") in",
							"auth.require = ( \"...\" => ( ..., \"method\" => \"...\") )");
					return HANDLER_ERROR;
				}
			}

			if (buffer_is_empty(realm)) {
				log_error_write(srv, __FILE__, __LINE__, "ss",
						"the realm field is missing in:",
						"auth.require = ( \"...\" => ( ..., \"realm\" => \"...\" ) )");
				return HANDLER_ERROR;
			}

			if (buffer_string_is_empty(require)) {
				log_error_write(srv, __FILE__, __LINE__, "ss",
						"the require field is missing or blank in:",
						"auth.require = ( \"...\" => ( ..., \"require\" => \"...\" ) )");
				return HANDLER_ERROR;
			}

			if (require) { /*(always true at this point)*/
				data_auth * const dauth = data_auth_init();
				buffer_copy_buffer(dauth->key, da_file->key);
				dauth->require->scheme = auth_scheme;
				buffer_copy_buffer(dauth->require->realm, realm);
				if (!mod_auth_require_parse(srv, dauth->require, require)) {
					dauth->free((data_unset *)dauth);
					return HANDLER_ERROR;
				}
				array_insert_unique(s->auth_require, (data_unset *)dauth);
			}
		}
	}

	return HANDLER_GO_ON;
}

#define PATCH(x) \
	p->conf.x = s->x;
static int mod_auth_patch_connection(server *srv, connection *con, plugin_data *p) {
	size_t i, j;
	plugin_config *s = p->config_storage[0];

	PATCH(auth_backend);
	PATCH(auth_require);
	PATCH(auth_extern_authn);

	/* skip the first, the global context */
	for (i = 1; i < srv->config_context->used; i++) {
		data_config *dc = (data_config *)srv->config_context->data[i];
		s = p->config_storage[i];

		/* condition didn't match */
		if (!config_check_cond(srv, con, dc)) continue;

		/* merge config */
		for (j = 0; j < dc->value->used; j++) {
			data_unset *du = dc->value->data[j];

			if (buffer_is_equal_string(du->key, CONST_STR_LEN("auth.backend"))) {
				PATCH(auth_backend);
			} else if (buffer_is_equal_string(du->key, CONST_STR_LEN("auth.require"))) {
				PATCH(auth_require);
			} else if (buffer_is_equal_string(du->key, CONST_STR_LEN("auth.extern-authn"))) {
				PATCH(auth_extern_authn);
			}
		}
	}

	return 0;
}
#undef PATCH

static handler_t mod_auth_uri_handler(server *srv, connection *con, void *p_d) {
	size_t k;
	plugin_data *p = p_d;

	mod_auth_patch_connection(srv, con, p);

	if (p->conf.auth_require == NULL) return HANDLER_GO_ON;

	/* search auth directives for first prefix match against URL path */
	for (k = 0; k < p->conf.auth_require->used; k++) {
		const data_auth * const dauth = (data_auth *)p->conf.auth_require->data[k];
		const buffer *path = dauth->key;

		if (buffer_string_length(con->uri.path) < buffer_string_length(path)) continue;

		/* if we have a case-insensitive FS we have to lower-case the URI here too */

		if (!con->conf.force_lowercase_filenames
		    ? 0 == strncmp(con->uri.path->ptr, path->ptr, buffer_string_length(path))
		    : 0 == strncasecmp(con->uri.path->ptr, path->ptr, buffer_string_length(path))) {
			const http_auth_scheme_t * const scheme = dauth->require->scheme;
			if (p->conf.auth_extern_authn) {
				buffer *vb = http_header_env_get(con, CONST_STR_LEN("REMOTE_USER"));
				if (NULL != vb && http_auth_match_rules(dauth->require, vb->ptr, NULL, NULL)) {
					return HANDLER_GO_ON;
				}
			}
			return scheme->checkfn(srv, con, scheme->p_d, dauth->require, p->conf.auth_backend);
		}
	}

	/* nothing to do for us */
	return HANDLER_GO_ON;
}

int mod_auth_plugin_init(plugin *p);
int mod_auth_plugin_init(plugin *p) {
	p->version     = LIGHTTPD_VERSION_ID;
	p->name        = buffer_init_string("auth");
	p->init        = mod_auth_init;
	p->set_defaults = mod_auth_set_defaults;
	p->handle_uri_clean = mod_auth_uri_handler;
	p->cleanup     = mod_auth_free;

	p->data        = NULL;

	return 0;
}




/*
 * auth schemes (basic, digest, extern)
 *
 * (could be in separate file from mod_auth.c as long as registration occurs)
 */

#include "base64.h"
#include "md5.h"
#include "rand.h"
#include "http_header.h"

static handler_t mod_auth_send_400_bad_request(server *srv, connection *con) {
	UNUSED(srv);

	/* a field was missing or invalid */
	con->http_status = 400; /* Bad Request */
	con->mode = DIRECT;

	return HANDLER_FINISHED;
}

static handler_t mod_auth_send_401_unauthorized_basic(server *srv, connection *con, buffer *realm) {
	con->http_status = 401;
	con->mode = DIRECT;

	buffer_copy_string_len(srv->tmp_buf, CONST_STR_LEN("Basic realm=\""));
	buffer_append_string_buffer(srv->tmp_buf, realm);
	buffer_append_string_len(srv->tmp_buf, CONST_STR_LEN("\", charset=\"UTF-8\""));

	http_header_response_set(con, HTTP_HEADER_OTHER, CONST_STR_LEN("WWW-Authenticate"), CONST_BUF_LEN(srv->tmp_buf));

	return HANDLER_FINISHED;
}

static handler_t mod_auth_check_basic(server *srv, connection *con, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend) {
	buffer *b = http_header_request_get(con, HTTP_HEADER_AUTHORIZATION, CONST_STR_LEN("Authorization"));
	buffer *username;
	char *pw;
	handler_t rc = HANDLER_UNSET;

	UNUSED(p_d);

	if (NULL == backend) {
		log_error_write(srv, __FILE__, __LINE__, "sb", "auth.backend not configured for", con->uri.path);
		con->http_status = 500;
		con->mode = DIRECT;
		return HANDLER_FINISHED;
	}

	if (NULL == b) {
		return mod_auth_send_401_unauthorized_basic(srv, con, require->realm);
	}

	if (0 != strncasecmp(b->ptr, "Basic ", sizeof("Basic ")-1)) {
		return mod_auth_send_400_bad_request(srv, con);
	}
      #ifdef __COVERITY__
	if (buffer_string_length(b) < sizeof("Basic ")-1) {
		return mod_auth_send_400_bad_request(srv, con);
	}
      #endif

	username = buffer_init();

	/* coverity[overflow_sink : FALSE] */
	if (!buffer_append_base64_decode(username, b->ptr+sizeof("Basic ")-1, buffer_string_length(b)-(sizeof("Basic ")-1), BASE64_STANDARD)) {
		log_error_write(srv, __FILE__, __LINE__, "sb", "decoding base64-string failed", username);

		buffer_free(username);
		return mod_auth_send_400_bad_request(srv, con);
	}

	/* r2 == user:password */
	if (NULL == (pw = strchr(username->ptr, ':'))) {
		log_error_write(srv, __FILE__, __LINE__, "sb", "missing ':' in", username);

		buffer_free(username);
		return mod_auth_send_400_bad_request(srv, con);
	}

	buffer_string_set_length(username, pw - username->ptr);
	pw++;

	rc = backend->basic(srv, con, backend->p_d, require, username, pw);
	switch (rc) {
	case HANDLER_GO_ON:
		http_auth_setenv(con, CONST_BUF_LEN(username), CONST_STR_LEN("Basic"));
		break;
	case HANDLER_WAIT_FOR_EVENT:
	case HANDLER_FINISHED:
		break;
	case HANDLER_ERROR:
	default:
		log_error_write(srv, __FILE__, __LINE__, "sbsBsB", "password doesn't match for", con->uri.path, "username:", username, ", IP:", con->dst_addr_buf);
		rc = HANDLER_UNSET;
		break;
	}

	buffer_free(username);
	return (HANDLER_UNSET != rc) ? rc : mod_auth_send_401_unauthorized_basic(srv, con, require->realm);
}

#define HASHLEN 16
#define HASHHEXLEN 32
typedef unsigned char HASH[HASHLEN];
typedef char HASHHEX[HASHHEXLEN+1];

static void CvtHex(const HASH Bin, char (*Hex)[33]) {
	li_tohex(*Hex, sizeof(*Hex), (const char*) Bin, 16);
}

typedef struct {
	const char *key;
	int key_len;
	char **ptr;
} digest_kv;

static handler_t mod_auth_send_401_unauthorized_digest(server *srv, connection *con, buffer *realm, int nonce_stale);

static handler_t mod_auth_check_digest(server *srv, connection *con, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend) {
	buffer *vb = http_header_request_get(con, HTTP_HEADER_AUTHORIZATION, CONST_STR_LEN("Authorization"));

	char a1[33];
	char a2[33];

	char *username = NULL;
	char *realm = NULL;
	char *nonce = NULL;
	char *uri = NULL;
	char *algorithm = NULL;
	char *qop = NULL;
	char *cnonce = NULL;
	char *nc = NULL;
	char *respons = NULL;

	char *e, *c;
	const char *m = NULL;
	int i;
	buffer *b;

	li_MD5_CTX Md5Ctx;
	HASH HA1;
	HASH HA2;
	HASH RespHash;
	HASHHEX HA2Hex;


	/* init pointers */
#define S(x) \
	x, sizeof(x)-1, NULL
	digest_kv dkv[10] = {
		{ S("username=") },
		{ S("realm=") },
		{ S("nonce=") },
		{ S("uri=") },
		{ S("algorithm=") },
		{ S("qop=") },
		{ S("cnonce=") },
		{ S("nc=") },
		{ S("response=") },

		{ NULL, 0, NULL }
	};
#undef S

	dkv[0].ptr = &username;
	dkv[1].ptr = &realm;
	dkv[2].ptr = &nonce;
	dkv[3].ptr = &uri;
	dkv[4].ptr = &algorithm;
	dkv[5].ptr = &qop;
	dkv[6].ptr = &cnonce;
	dkv[7].ptr = &nc;
	dkv[8].ptr = &respons;

	UNUSED(p_d);

	if (NULL == backend) {
		log_error_write(srv, __FILE__, __LINE__, "sb", "auth.backend not configured for", con->uri.path);
		con->http_status = 500;
		con->mode = DIRECT;
		return HANDLER_FINISHED;
	}

	if (NULL == vb) {
		return mod_auth_send_401_unauthorized_digest(srv, con, require->realm, 0);
	}

	if (0 != strncasecmp(vb->ptr, "Digest ", sizeof("Digest ")-1)) {
		return mod_auth_send_400_bad_request(srv, con);
	} else {
		size_t n = buffer_string_length(vb);
	      #ifdef __COVERITY__
		if (n < sizeof("Digest ")-1) {
			return mod_auth_send_400_bad_request(srv, con);
		}
	      #endif
		n -= (sizeof("Digest ")-1);
		b = buffer_init();
		buffer_copy_string_len(b,vb->ptr+sizeof("Digest ")-1,n);
	}

	/* parse credentials from client */
	for (c = b->ptr; *c; c++) {
		/* skip whitespaces */
		while (*c == ' ' || *c == '\t') c++;
		if (!*c) break;

		for (i = 0; dkv[i].key; i++) {
			if ((0 == strncmp(c, dkv[i].key, dkv[i].key_len))) {
				if ((c[dkv[i].key_len] == '"') &&
				    (NULL != (e = strchr(c + dkv[i].key_len + 1, '"')))) {
					/* value with "..." */
					*(dkv[i].ptr) = c + dkv[i].key_len + 1;
					c = e;

					*e = '\0';
				} else if (NULL != (e = strchr(c + dkv[i].key_len, ','))) {
					/* value without "...", terminated by ',' */
					*(dkv[i].ptr) = c + dkv[i].key_len;
					c = e;

					*e = '\0';
				} else {
					/* value without "...", terminated by EOL */
					*(dkv[i].ptr) = c + dkv[i].key_len;
					c += strlen(c) - 1;
				}
				break;
			}
		}
	}

	/* check if everything is transmitted */
	if (!username ||
	    !realm ||
	    !nonce ||
	    !uri ||
	    (qop && (!nc || !cnonce)) ||
	    !respons ) {
		/* missing field */

		log_error_write(srv, __FILE__, __LINE__, "s",
				"digest: missing field");

		buffer_free(b);
		return mod_auth_send_400_bad_request(srv, con);
	}

	if (!buffer_is_equal_string(require->realm, realm, strlen(realm))) {
		log_error_write(srv, __FILE__, __LINE__, "s",
				"digest: realm mismatch");
		buffer_free(b);
		return mod_auth_send_401_unauthorized_digest(srv, con, require->realm, 0);
	}

	/**
	 * protect the md5-sess against missing cnonce and nonce
	 */
	if (algorithm &&
	    0 == strcasecmp(algorithm, "md5-sess") &&
	    (!nonce || !cnonce)) {
		log_error_write(srv, __FILE__, __LINE__, "s",
				"digest: (md5-sess: missing field");

		buffer_free(b);
		return mod_auth_send_400_bad_request(srv, con);
	}

	if (qop && strcasecmp(qop, "auth-int") == 0) {
		log_error_write(srv, __FILE__, __LINE__, "s",
				"digest: qop=auth-int not supported");

		buffer_free(b);
		return mod_auth_send_400_bad_request(srv, con);
	}

	m = get_http_method_name(con->request.http_method);
	force_assert(m);

	/* detect if attacker is attempting to reuse valid digest for one uri
	 * on a different request uri.  Might also happen if intermediate proxy
	 * altered client request line.  (Altered request would not result in
	 * the same digest as that calculated by the client.)
	 * Internal redirects such as with mod_rewrite will modify request uri.
	 * Reauthentication is done to detect crossing auth realms, but this
	 * uri validation step is bypassed.  con->request.orig_uri is original
	 * uri sent in client request. */
	{
		const size_t ulen = strlen(uri);
		const size_t rlen = buffer_string_length(con->request.orig_uri);
		if (!buffer_is_equal_string(con->request.orig_uri, uri, ulen)
		    && !(rlen < ulen && 0 == memcmp(con->request.orig_uri->ptr, uri, rlen) && uri[rlen] == '?')) {
			log_error_write(srv, __FILE__, __LINE__, "sbsssB",
					"digest: auth failed: uri mismatch (", con->request.orig_uri, "!=", uri, "), IP:", con->dst_addr_buf);
			buffer_free(b);
			return mod_auth_send_400_bad_request(srv, con);
		}
	}

	/* password-string == HA1 */
	switch (backend->digest(srv, con, backend->p_d, username, realm, HA1)) {
	case HANDLER_GO_ON:
		break;
	case HANDLER_WAIT_FOR_EVENT:
		buffer_free(b);
		return HANDLER_WAIT_FOR_EVENT;
	case HANDLER_FINISHED:
		buffer_free(b);
		return HANDLER_FINISHED;
	case HANDLER_ERROR:
	default:
		buffer_free(b);
		return mod_auth_send_401_unauthorized_digest(srv, con, require->realm, 0);
	}

	if (algorithm &&
	    strcasecmp(algorithm, "md5-sess") == 0) {
		li_MD5_Init(&Md5Ctx);
		/* Errata ID 1649: http://www.rfc-editor.org/errata_search.php?rfc=2617 */
		CvtHex(HA1, &a1);
		li_MD5_Update(&Md5Ctx, (unsigned char *)a1, HASHHEXLEN);
		li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
		li_MD5_Update(&Md5Ctx, (unsigned char *)nonce, strlen(nonce));
		li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
		li_MD5_Update(&Md5Ctx, (unsigned char *)cnonce, strlen(cnonce));
		li_MD5_Final(HA1, &Md5Ctx);
	}

	CvtHex(HA1, &a1);

	/* calculate H(A2) */
	li_MD5_Init(&Md5Ctx);
	li_MD5_Update(&Md5Ctx, (unsigned char *)m, strlen(m));
	li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
	li_MD5_Update(&Md5Ctx, (unsigned char *)uri, strlen(uri));
	/* qop=auth-int not supported, already checked above */
/*
	if (qop && strcasecmp(qop, "auth-int") == 0) {
		li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
		li_MD5_Update(&Md5Ctx, (unsigned char *) [body checksum], HASHHEXLEN);
	}
*/
	li_MD5_Final(HA2, &Md5Ctx);
	CvtHex(HA2, &HA2Hex);

	/* calculate response */
	li_MD5_Init(&Md5Ctx);
	li_MD5_Update(&Md5Ctx, (unsigned char *)a1, HASHHEXLEN);
	li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
	li_MD5_Update(&Md5Ctx, (unsigned char *)nonce, strlen(nonce));
	li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
	if (qop && *qop) {
		li_MD5_Update(&Md5Ctx, (unsigned char *)nc, strlen(nc));
		li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
		li_MD5_Update(&Md5Ctx, (unsigned char *)cnonce, strlen(cnonce));
		li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
		li_MD5_Update(&Md5Ctx, (unsigned char *)qop, strlen(qop));
		li_MD5_Update(&Md5Ctx, CONST_STR_LEN(":"));
	};
	li_MD5_Update(&Md5Ctx, (unsigned char *)HA2Hex, HASHHEXLEN);
	li_MD5_Final(RespHash, &Md5Ctx);
	CvtHex(RespHash, &a2);

	if (0 != strcmp(a2, respons)) {
		/* digest not ok */
		log_error_write(srv, __FILE__, __LINE__, "sssB",
				"digest: auth failed for ", username, ": wrong password, IP:", con->dst_addr_buf);

		buffer_free(b);
		return mod_auth_send_401_unauthorized_digest(srv, con, require->realm, 0);
	}

	/* value is our allow-rules */
	if (!http_auth_match_rules(require, username, NULL, NULL)) {
		buffer_free(b);
		return mod_auth_send_401_unauthorized_digest(srv, con, require->realm, 0);
	}

	/* check age of nonce.  Note, random data is used in nonce generation
	 * in mod_auth_send_401_unauthorized_digest().  If that were replaced
	 * with nanosecond time, then nonce secret would remain unique enough
	 * for the purposes of Digest auth, and would be reproducible (and
	 * verifiable) if nanoseconds were inclued with seconds as part of the
	 * nonce "timestamp:secret".  Since that is not done, timestamp in
	 * nonce could theoretically be modified and still produce same md5sum,
	 * but that is highly unlikely within a 10 min (moving) window of valid
	 * time relative to current time (now) */
	{
		time_t ts = 0;
		const unsigned char * const nonce_uns = (unsigned char *)nonce;
		for (i = 0; i < 8 && light_isxdigit(nonce_uns[i]); ++i) {
			ts = (ts << 4) + hex2int(nonce_uns[i]);
		}
		if (nonce[i] != ':'
		    || ts > srv->cur_ts || srv->cur_ts - ts > 600) { /*(10 mins)*/
			/* nonce is stale; have client regenerate digest */
			buffer_free(b);
			return mod_auth_send_401_unauthorized_digest(srv, con, require->realm, 1);
		} /*(future: might send nextnonce when expiration is imminent)*/
	}

	http_auth_setenv(con, username, strlen(username), CONST_STR_LEN("Digest"));

	buffer_free(b);

	return HANDLER_GO_ON;
}

static handler_t mod_auth_send_401_unauthorized_digest(server *srv, connection *con, buffer *realm, int nonce_stale) {
	li_MD5_CTX Md5Ctx;
	HASH h;
	char hh[33];

	force_assert(33 >= LI_ITOSTRING_LENGTH); /*(buffer used for both li_itostrn() and CvtHex())*/

	/* generate nonce */

	/* generate shared-secret */
	li_MD5_Init(&Md5Ctx);

	li_itostrn(hh, sizeof(hh), srv->cur_ts);
	li_MD5_Update(&Md5Ctx, (unsigned char *)hh, strlen(hh));
	li_itostrn(hh, sizeof(hh), li_rand_pseudo());
	li_MD5_Update(&Md5Ctx, (unsigned char *)hh, strlen(hh));

	li_MD5_Final(h, &Md5Ctx);

	CvtHex(h, &hh);

	/* generate WWW-Authenticate */

	con->http_status = 401;
	con->mode = DIRECT;

	buffer_copy_string_len(srv->tmp_buf, CONST_STR_LEN("Digest realm=\""));
	buffer_append_string_buffer(srv->tmp_buf, realm);
	buffer_append_string_len(srv->tmp_buf, CONST_STR_LEN("\", charset=\"UTF-8\", nonce=\""));
	buffer_append_uint_hex(srv->tmp_buf, (uintmax_t)srv->cur_ts);
	buffer_append_string_len(srv->tmp_buf, CONST_STR_LEN(":"));
	buffer_append_string(srv->tmp_buf, hh);
	buffer_append_string_len(srv->tmp_buf, CONST_STR_LEN("\", qop=\"auth\""));
	if (nonce_stale) {
		buffer_append_string_len(srv->tmp_buf, CONST_STR_LEN(", stale=true"));
	}

	http_header_response_set(con, HTTP_HEADER_OTHER, CONST_STR_LEN("WWW-Authenticate"), CONST_BUF_LEN(srv->tmp_buf));

	return HANDLER_FINISHED;
}

static handler_t mod_auth_check_extern(server *srv, connection *con, void *p_d, const struct http_auth_require_t *require, const struct http_auth_backend_t *backend) {
	/* require REMOTE_USER already set */
	buffer *vb = http_header_env_get(con, CONST_STR_LEN("REMOTE_USER"));
	UNUSED(srv);
	UNUSED(p_d);
	UNUSED(backend);
	if (NULL != vb && http_auth_match_rules(require, vb->ptr, NULL, NULL)) {
		return HANDLER_GO_ON;
	} else {
		con->http_status = 401;
		con->mode = DIRECT;
		return HANDLER_FINISHED;
	}
}