/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "apr_strings.h"
#include "apr_lib.h"                /* for apr_isspace */
#include "apr_base64.h"             /* for apr_base64_decode et al */
#define APR_WANT_STRFUNC            /* for strcasecmp */
#include "apr_want.h"

#include "ap_config.h"
#include "httpd.h"
#include "http_config.h"
#include "http_core.h"
#include "http_log.h"
#include "http_protocol.h"
#include "http_request.h"
#include "ap_provider.h"
#include "util_md5.h"
#include "ap_expr.h"

#include "mod_auth.h"
#include "mod_session.h"
#include "mod_request.h"

#define FORM_LOGIN_HANDLER "form-login-handler"
#define FORM_LOGOUT_HANDLER "form-logout-handler"
#define FORM_REDIRECT_HANDLER "form-redirect-handler"
#define MOD_AUTH_FORM_HASH "site"

static APR_OPTIONAL_FN_TYPE(ap_session_load) *ap_session_load_fn = NULL;
static APR_OPTIONAL_FN_TYPE(ap_session_get)  *ap_session_get_fn = NULL;
static APR_OPTIONAL_FN_TYPE(ap_session_set)  *ap_session_set_fn = NULL;

static void (*ap_request_insert_filter_fn) (request_rec * r) = NULL;
static void (*ap_request_remove_filter_fn) (request_rec * r) = NULL;

typedef struct {
    authn_provider_list *providers;
    char *dir;
    int authoritative;
    int authoritative_set;
    const char *site;
    int site_set;
    const char *username;
    int username_set;
    const char *password;
    int password_set;
    apr_size_t form_size;
    int form_size_set;
    int fakebasicauth;
    int fakebasicauth_set;
    const char *location;
    int location_set;
    const char *method;
    int method_set;
    const char *mimetype;
    int mimetype_set;
    const char *body;
    int body_set;
    int disable_no_store;
    int disable_no_store_set;
    ap_expr_info_t *loginsuccess;
    int loginsuccess_set;
    ap_expr_info_t *loginrequired;
    int loginrequired_set;
    ap_expr_info_t *logout;
    int logout_set;
} auth_form_config_rec;

static void *create_auth_form_dir_config(apr_pool_t * p, char *d)
{
    auth_form_config_rec *conf = apr_pcalloc(p, sizeof(*conf));

    conf->dir = d;
    /* Any failures are fatal. */
    conf->authoritative = 1;

    /* form size defaults to 8k */
    conf->form_size = HUGE_STRING_LEN;

    /* default form field names */
    conf->username = "httpd_username";
    conf->password = "httpd_password";
    conf->location = "httpd_location";
    conf->method = "httpd_method";
    conf->mimetype = "httpd_mimetype";
    conf->body = "httpd_body";

    return conf;
}

static void *merge_auth_form_dir_config(apr_pool_t * p, void *basev, void *addv)
{
    auth_form_config_rec *new = (auth_form_config_rec *) apr_pcalloc(p, sizeof(auth_form_config_rec));
    auth_form_config_rec *add = (auth_form_config_rec *) addv;
    auth_form_config_rec *base = (auth_form_config_rec *) basev;

    new->providers = !add->providers ? base->providers : add->providers;
    new->authoritative = (add->authoritative_set == 0) ? base->authoritative : add->authoritative;
    new->authoritative_set = add->authoritative_set || base->authoritative_set;
    new->site = (add->site_set == 0) ? base->site : add->site;
    new->site_set = add->site_set || base->site_set;
    new->username = (add->username_set == 0) ? base->username : add->username;
    new->username_set = add->username_set || base->username_set;
    new->password = (add->password_set == 0) ? base->password : add->password;
    new->password_set = add->password_set || base->password_set;
    new->location = (add->location_set == 0) ? base->location : add->location;
    new->location_set = add->location_set || base->location_set;
    new->form_size = (add->form_size_set == 0) ? base->form_size : add->form_size;
    new->form_size_set = add->form_size_set || base->form_size_set;
    new->fakebasicauth = (add->fakebasicauth_set == 0) ? base->fakebasicauth : add->fakebasicauth;
    new->fakebasicauth_set = add->fakebasicauth_set || base->fakebasicauth_set;
    new->method = (add->method_set == 0) ? base->method : add->method;
    new->method_set = add->method_set || base->method_set;
    new->mimetype = (add->mimetype_set == 0) ? base->mimetype : add->mimetype;
    new->mimetype_set = add->mimetype_set || base->mimetype_set;
    new->body = (add->body_set == 0) ? base->body : add->body;
    new->body_set = add->body_set || base->body_set;
    new->disable_no_store = (add->disable_no_store_set == 0) ? base->disable_no_store : add->disable_no_store;
    new->disable_no_store_set = add->disable_no_store_set || base->disable_no_store_set;
    new->loginsuccess = (add->loginsuccess_set == 0) ? base->loginsuccess : add->loginsuccess;
    new->loginsuccess_set = add->loginsuccess_set || base->loginsuccess_set;
    new->loginrequired = (add->loginrequired_set == 0) ? base->loginrequired : add->loginrequired;
    new->loginrequired_set = add->loginrequired_set || base->loginrequired_set;
    new->logout = (add->logout_set == 0) ? base->logout : add->logout;
    new->logout_set = add->logout_set || base->logout_set;

    return new;
}

static const char *add_authn_provider(cmd_parms * cmd, void *config,
                                           const char *arg)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    authn_provider_list *newp;

    newp = apr_pcalloc(cmd->pool, sizeof(authn_provider_list));
    newp->provider_name = arg;

    /* lookup and cache the actual provider now */
    newp->provider = ap_lookup_provider(AUTHN_PROVIDER_GROUP,
                                        newp->provider_name,
                                        AUTHN_PROVIDER_VERSION);

    if (newp->provider == NULL) {
        /*
         * by the time they use it, the provider should be loaded and
         * registered with us.
         */
        return apr_psprintf(cmd->pool,
                            "Unknown Authn provider: %s",
                            newp->provider_name);
    }

    if (!newp->provider->check_password) {
        /* if it doesn't provide the appropriate function, reject it */
        return apr_psprintf(cmd->pool,
                            "The '%s' Authn provider doesn't support "
                            "Form Authentication", newp->provider_name);
    }

    /* Add it to the list now. */
    if (!conf->providers) {
        conf->providers = newp;
    }
    else {
        authn_provider_list *last = conf->providers;

        while (last->next) {
            last = last->next;
        }
        last->next = newp;
    }

    return NULL;
}

/**
 * Sanity check a given string that it exists, is not empty,
 * and does not contain special characters.
 */
static const char *check_string(cmd_parms * cmd, const char *string)
{
    if (!string || !*string || ap_strchr_c(string, '=') || ap_strchr_c(string, '&')) {
        return apr_pstrcat(cmd->pool, cmd->directive->directive,
                           " cannot be empty, or contain '=' or '&'.",
                           NULL);
    }
    return NULL;
}

static const char *set_cookie_form_location(cmd_parms * cmd, void *config, const char *location)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->location = location;
    conf->location_set = 1;
    return check_string(cmd, location);
}

static const char *set_cookie_form_username(cmd_parms * cmd, void *config, const char *username)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->username = username;
    conf->username_set = 1;
    return check_string(cmd, username);
}

static const char *set_cookie_form_password(cmd_parms * cmd, void *config, const char *password)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->password = password;
    conf->password_set = 1;
    return check_string(cmd, password);
}

static const char *set_cookie_form_method(cmd_parms * cmd, void *config, const char *method)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->method = method;
    conf->method_set = 1;
    return check_string(cmd, method);
}

static const char *set_cookie_form_mimetype(cmd_parms * cmd, void *config, const char *mimetype)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->mimetype = mimetype;
    conf->mimetype_set = 1;
    return check_string(cmd, mimetype);
}

static const char *set_cookie_form_body(cmd_parms * cmd, void *config, const char *body)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->body = body;
    conf->body_set = 1;
    return check_string(cmd, body);
}

static const char *set_cookie_form_size(cmd_parms * cmd, void *config,
                                             const char *arg)
{
    auth_form_config_rec *conf = config;
    apr_off_t size;

    if (APR_SUCCESS != apr_strtoff(&size, arg, NULL, 10)
        || size < 0 || size > APR_SIZE_MAX) {
        return "AuthCookieFormSize must be a size in bytes, or zero.";
    }
    conf->form_size = (apr_size_t)size;
    conf->form_size_set = 1;

    return NULL;
}

static const char *set_login_required_location(cmd_parms * cmd, void *config, const char *loginrequired)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    const char *err;

    conf->loginrequired = ap_expr_parse_cmd(cmd, loginrequired, AP_EXPR_FLAG_STRING_RESULT,
                                        &err, NULL);
    if (err) {
        return apr_psprintf(cmd->pool,
                            "Could not parse login required expression '%s': %s",
                            loginrequired, err);
    }
    conf->loginrequired_set = 1;

    return NULL;
}

static const char *set_login_success_location(cmd_parms * cmd, void *config, const char *loginsuccess)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    const char *err;

    conf->loginsuccess = ap_expr_parse_cmd(cmd, loginsuccess, AP_EXPR_FLAG_STRING_RESULT,
                                        &err, NULL);
    if (err) {
        return apr_psprintf(cmd->pool,
                            "Could not parse login success expression '%s': %s",
                            loginsuccess, err);
    }
    conf->loginsuccess_set = 1;

    return NULL;
}

static const char *set_logout_location(cmd_parms * cmd, void *config, const char *logout)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    const char *err;

    conf->logout = ap_expr_parse_cmd(cmd, logout, AP_EXPR_FLAG_STRING_RESULT,
                                        &err, NULL);
    if (err) {
        return apr_psprintf(cmd->pool,
                            "Could not parse logout required expression '%s': %s",
                            logout, err);
    }
    conf->logout_set = 1;

    return NULL;
}

static const char *set_site_passphrase(cmd_parms * cmd, void *config, const char *site)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->site = site;
    conf->site_set = 1;
    return NULL;
}

static const char *set_authoritative(cmd_parms * cmd, void *config, int flag)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->authoritative = flag;
    conf->authoritative_set = 1;
    return NULL;
}

static const char *set_fake_basic_auth(cmd_parms * cmd, void *config, int flag)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->fakebasicauth = flag;
    conf->fakebasicauth_set = 1;
    return NULL;
}

static const char *set_disable_no_store(cmd_parms * cmd, void *config, int flag)
{
    auth_form_config_rec *conf = (auth_form_config_rec *) config;
    conf->disable_no_store = flag;
    conf->disable_no_store_set = 1;
    return NULL;
}

static const command_rec auth_form_cmds[] =
{
    AP_INIT_ITERATE("AuthFormProvider", add_authn_provider, NULL, OR_AUTHCFG,
                    "specify the auth providers for a directory or location"),
    AP_INIT_TAKE1("AuthFormUsername", set_cookie_form_username, NULL, OR_AUTHCFG,
                  "The field of the login form carrying the username"),
    AP_INIT_TAKE1("AuthFormPassword", set_cookie_form_password, NULL, OR_AUTHCFG,
                  "The field of the login form carrying the password"),
    AP_INIT_TAKE1("AuthFormLocation", set_cookie_form_location, NULL, OR_AUTHCFG,
                  "The field of the login form carrying the URL to redirect on "
                  "successful login."),
    AP_INIT_TAKE1("AuthFormMethod", set_cookie_form_method, NULL, OR_AUTHCFG,
                  "The field of the login form carrying the original request method."),
    AP_INIT_TAKE1("AuthFormMimetype", set_cookie_form_mimetype, NULL, OR_AUTHCFG,
                  "The field of the login form carrying the original request mimetype."),
    AP_INIT_TAKE1("AuthFormBody", set_cookie_form_body, NULL, OR_AUTHCFG,
                  "The field of the login form carrying the urlencoded original request "
                  "body."),
    AP_INIT_TAKE1("AuthFormSize", set_cookie_form_size, NULL, ACCESS_CONF,
                  "Maximum size of body parsed by the form parser"),
    AP_INIT_TAKE1("AuthFormLoginRequiredLocation", set_login_required_location,
                  NULL, OR_AUTHCFG,
                  "If set, redirect the browser to this URL rather than "
                  "return 401 Not Authorized."),
    AP_INIT_TAKE1("AuthFormLoginSuccessLocation", set_login_success_location,
                  NULL, OR_AUTHCFG,
                  "If set, redirect the browser to this URL when a login "
                  "processed by the login handler is successful."),
    AP_INIT_TAKE1("AuthFormLogoutLocation", set_logout_location,
                  NULL, OR_AUTHCFG,
                  "The URL of the logout successful page. An attempt to access an "
                  "URL handled by the handler " FORM_LOGOUT_HANDLER " will result "
                  "in an redirect to this page after logout."),
    AP_INIT_TAKE1("AuthFormSitePassphrase", set_site_passphrase,
                  NULL, OR_AUTHCFG,
                  "If set, use this passphrase to determine whether the user should "
                  "be authenticated. Bypasses the user authentication check on "
                  "every website hit, and is useful for high traffic sites."),
    AP_INIT_FLAG("AuthFormAuthoritative", set_authoritative,
                 NULL, OR_AUTHCFG,
                 "Set to 'Off' to allow access control to be passed along to "
                 "lower modules if the UserID is not known to this module"),
    AP_INIT_FLAG("AuthFormFakeBasicAuth", set_fake_basic_auth,
                 NULL, OR_AUTHCFG,
                 "Set to 'On' to pass through authentication to the rest of the "
                 "server as a basic authentication header."),
    AP_INIT_FLAG("AuthFormDisableNoStore", set_disable_no_store,
                 NULL, OR_AUTHCFG,
                 "Set to 'on' to stop the sending of a Cache-Control no-store header with "
                 "the login screen. This allows the browser to cache the credentials, but "
                 "at the risk of it being possible for the login form to be resubmitted "
                 "and revealed to the backend server through XSS. Use at own risk."),
    {NULL}
};

module AP_MODULE_DECLARE_DATA auth_form_module;

static void note_cookie_auth_failure(request_rec * r)
{
    auth_form_config_rec *conf = ap_get_module_config(r->per_dir_config,
                                                      &auth_form_module);

    if (conf->location && ap_strchr_c(conf->location, ':')) {
        apr_table_setn(r->err_headers_out, "Location", conf->location);
    }
}

static int hook_note_cookie_auth_failure(request_rec * r,
                                         const char *auth_type)
{
    if (ap_cstr_casecmp(auth_type, "form"))
        return DECLINED;

    note_cookie_auth_failure(r);
    return OK;
}

/**
 * Set the auth username and password into the main request
 * notes table.
 */
static void set_notes_auth(request_rec * r,
                                const char *user, const char *pw,
                                const char *method, const char *mimetype)
{
    apr_table_t *notes = NULL;
    const char *authname;

    /* find the main request */
    while (r->main) {
        r = r->main;
    }
    /* find the first redirect */
    while (r->prev) {
        r = r->prev;
    }
    notes = r->notes;

    /* have we isolated the user and pw before? */
    authname = ap_auth_name(r);
    if (user) {
        apr_table_setn(notes, apr_pstrcat(r->pool, authname, "-user", NULL), user);
    }
    if (pw) {
        apr_table_setn(notes, apr_pstrcat(r->pool, authname, "-pw", NULL), pw);
    }
    if (method) {
        apr_table_setn(notes, apr_pstrcat(r->pool, authname, "-method", NULL), method);
    }
    if (mimetype) {
        apr_table_setn(notes, apr_pstrcat(r->pool, authname, "-mimetype", NULL), mimetype);
    }

}

/**
 * Get the auth username and password from the main request
 * notes table, if present.
 */
static void get_notes_auth(request_rec *r,
                           const char **user, const char **pw,
                           const char **method, const char **mimetype)
{
    const char *authname;
    request_rec *m = r;

    /* find the main request */
    while (m->main) {
        m = m->main;
    }
    /* find the first redirect */
    while (m->prev) {
        m = m->prev;
    }

    /* have we isolated the user and pw before? */
    authname = ap_auth_name(m);
    if (user) {
        *user = (char *) apr_table_get(m->notes, apr_pstrcat(m->pool, authname, "-user", NULL));
    }
    if (pw) {
        *pw = (char *) apr_table_get(m->notes, apr_pstrcat(m->pool, authname, "-pw", NULL));
    }
    if (method) {
        *method = (char *) apr_table_get(m->notes, apr_pstrcat(m->pool, authname, "-method", NULL));
    }
    if (mimetype) {
        *mimetype = (char *) apr_table_get(m->notes, apr_pstrcat(m->pool, authname, "-mimetype", NULL));
    }

    /* set the user, even though the user is unauthenticated at this point */
    if (user && *user) {
        r->user = (char *) *user;
    }

    ap_log_rerror(APLOG_MARK, APLOG_TRACE1, 0, r,
                  "from notes: user: %s, pw: %s, method: %s, mimetype: %s",
                  user ? *user : "<null>", pw ? *pw : "<null>",
                  method ? *method : "<null>", mimetype ? *mimetype : "<null>");

}

/**
 * Set the auth username and password into the session.
 *
 * If either the username, or the password are NULL, the username
 * and/or password will be removed from the session.
 */
static apr_status_t set_session_auth(request_rec * r,
                                     const char *user, const char *pw, const char *site)
{
    const char *hash = NULL;
    const char *authname = ap_auth_name(r);
    session_rec *z = NULL;

    if (site) {
        hash = ap_md5(r->pool,
                      (unsigned char *) apr_pstrcat(r->pool, user, ":", site, NULL));
    }

    ap_session_load_fn(r, &z);
    ap_session_set_fn(r, z, apr_pstrcat(r->pool, authname, "-" MOD_SESSION_USER, NULL), user);
    ap_session_set_fn(r, z, apr_pstrcat(r->pool, authname, "-" MOD_SESSION_PW, NULL), pw);
    ap_session_set_fn(r, z, apr_pstrcat(r->pool, authname, "-" MOD_AUTH_FORM_HASH, NULL), hash);

    return APR_SUCCESS;

}

/**
 * Get the auth username and password from the main request
 * notes table, if present.
 */
static apr_status_t get_session_auth(request_rec * r,
                                     const char **user, const char **pw, const char **hash)
{
    const char *authname = ap_auth_name(r);
    session_rec *z = NULL;

    ap_session_load_fn(r, &z);

    if (user) {
        ap_session_get_fn(r, z, apr_pstrcat(r->pool, authname, "-" MOD_SESSION_USER, NULL), user);
    }
    if (pw) {
        ap_session_get_fn(r, z, apr_pstrcat(r->pool, authname, "-" MOD_SESSION_PW, NULL), pw);
    }
    if (hash) {
        ap_session_get_fn(r, z, apr_pstrcat(r->pool, authname, "-" MOD_AUTH_FORM_HASH, NULL), hash);
    }

    /* set the user, even though the user is unauthenticated at this point */
    if (user && *user) {
        r->user = (char *) *user;
    }

    ap_log_rerror(APLOG_MARK, APLOG_TRACE1, 0, r,
                  "from session: " MOD_SESSION_USER ": %s, " MOD_SESSION_PW
                  ": %s, " MOD_AUTH_FORM_HASH ": %s",
                  user ? *user : "<null>", pw ? *pw : "<null>",
                  hash ? *hash : "<null>");

    return APR_SUCCESS;

}

/**
 * Isolate the username and password in a POSTed form with the
 * username in the "username" field, and the password in the
 * "password" field.
 *
 * If either the username or the password is missing, this
 * function will return HTTP_UNAUTHORIZED.
 *
 * The location field is considered optional, and will be returned
 * if present.
 */
static int get_form_auth(request_rec * r,
                             const char *username,
                             const char *password,
                             const char *location,
                             const char *method,
                             const char *mimetype,
                             const char *body,
                             const char **sent_user,
                             const char **sent_pw,
                             const char **sent_loc,
                             const char **sent_method,
                             const char **sent_mimetype,
                             apr_bucket_brigade **sent_body,
                             auth_form_config_rec * conf)
{
    /* sanity check - are we a POST request? */

    /* find the username and password in the form */
    apr_array_header_t *pairs = NULL;
    apr_off_t len;
    apr_size_t size;
    int res;
    char *buffer;

    /* have we isolated the user and pw before? */
    get_notes_auth(r, sent_user, sent_pw, sent_method, sent_mimetype);
    if (sent_user && *sent_user && sent_pw && *sent_pw) {
        return OK;
    }

    res = ap_parse_form_data(r, NULL, &pairs, -1, conf->form_size);
    if (res != OK) {
        return res;
    }
    while (pairs && !apr_is_empty_array(pairs)) {
        ap_form_pair_t *pair = (ap_form_pair_t *) apr_array_pop(pairs);
        if (username && !strcmp(pair->name, username) && sent_user) {
            apr_brigade_length(pair->value, 1, &len);
            size = (apr_size_t) len;
            buffer = apr_palloc(r->pool, size + 1);
            apr_brigade_flatten(pair->value, buffer, &size);
            buffer[len] = 0;
            *sent_user = buffer;
        }
        else if (password && !strcmp(pair->name, password) && sent_pw) {
            apr_brigade_length(pair->value, 1, &len);
            size = (apr_size_t) len;
            buffer = apr_palloc(r->pool, size + 1);
            apr_brigade_flatten(pair->value, buffer, &size);
            buffer[len] = 0;
            *sent_pw = buffer;
        }
        else if (location && !strcmp(pair->name, location) && sent_loc) {
            apr_brigade_length(pair->value, 1, &len);
            size = (apr_size_t) len;
            buffer = apr_palloc(r->pool, size + 1);
            apr_brigade_flatten(pair->value, buffer, &size);
            buffer[len] = 0;
            *sent_loc = buffer;
        }
        else if (method && !strcmp(pair->name, method) && sent_method) {
            apr_brigade_length(pair->value, 1, &len);
            size = (apr_size_t) len;
            buffer = apr_palloc(r->pool, size + 1);
            apr_brigade_flatten(pair->value, buffer, &size);
            buffer[len] = 0;
            *sent_method = buffer;
        }
        else if (mimetype && !strcmp(pair->name, mimetype) && sent_mimetype) {
            apr_brigade_length(pair->value, 1, &len);
            size = (apr_size_t) len;
            buffer = apr_palloc(r->pool, size + 1);
            apr_brigade_flatten(pair->value, buffer, &size);
            buffer[len] = 0;
            *sent_mimetype = buffer;
        }
        else if (body && !strcmp(pair->name, body) && sent_body) {
            *sent_body = pair->value;
        }
    }

    ap_log_rerror(APLOG_MARK, APLOG_TRACE1, 0, r,
                  "from form: user: %s, pw: %s, method: %s, mimetype: %s, location: %s",
                  sent_user ? *sent_user : "<null>", sent_pw ? *sent_pw : "<null>",
                  sent_method ? *sent_method : "<null>",
                  sent_mimetype ? *sent_mimetype : "<null>",
                  sent_loc ? *sent_loc : "<null>");

    /* set the user, even though the user is unauthenticated at this point */
    if (sent_user && *sent_user) {
        r->user = (char *) *sent_user;
    }

    /* a missing username or missing password means auth denied */
    if (!sent_user || !*sent_user) {

        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(02982)
                      "form parsed, but username field '%s' was missing or empty, unauthorized",
                      username);

        return HTTP_UNAUTHORIZED;
    }
    if (!sent_pw || !*sent_pw) {

        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(02983)
                      "form parsed, but password field '%s' was missing or empty, unauthorized",
                      password);

        return HTTP_UNAUTHORIZED;
    }

    /*
     * save away the username, password, mimetype and method, so that they
     * are available should the auth need to be run again.
     */
    set_notes_auth(r, *sent_user, *sent_pw, sent_method ? *sent_method : NULL,
                   sent_mimetype ? *sent_mimetype : NULL);

    return OK;
}

/* These functions return 0 if client is OK, and proper error status
 * if not... either HTTP_UNAUTHORIZED, if we made a check, and it failed, or
 * HTTP_INTERNAL_SERVER_ERROR, if things are so totally confused that we
 * couldn't figure out how to tell if the client is authorized or not.
 *
 * If they return DECLINED, and all other modules also decline, that's
 * treated by the server core as a configuration error, logged and
 * reported as such.
 */


/**
 * Given a username and site passphrase hash from the session, determine
 * whether the site passphrase is valid for this session.
 *
 * If the site passphrase is NULL, or if the sent_hash is NULL, this
 * function returns DECLINED.
 *
 * If the site passphrase hash does not match the sent hash, this function
 * returns AUTH_USER_NOT_FOUND.
 *
 * On success, returns OK.
 */
static int check_site(request_rec * r, const char *site, const char *sent_user, const char *sent_hash)
{

    if (site && sent_user && sent_hash) {
        const char *hash = ap_md5(r->pool,
                      (unsigned char *) apr_pstrcat(r->pool, sent_user, ":", site, NULL));

        if (!strcmp(sent_hash, hash)) {
            return OK;
        }
        else {
            return AUTH_USER_NOT_FOUND;
        }
    }

    return DECLINED;

}

/**
 * Given a username and password (extracted externally from a cookie), run
 * the authnz hooks to determine whether this request is authorized.
 *
 * Return an HTTP code.
 */
static int check_authn(request_rec * r, const char *sent_user, const char *sent_pw)
{
    authn_status auth_result;
    authn_provider_list *current_provider;
    auth_form_config_rec *conf = ap_get_module_config(r->per_dir_config,
                                                      &auth_form_module);

    current_provider = conf->providers;
    do {
        const authn_provider *provider;

        /*
         * For now, if a provider isn't set, we'll be nice and use the file
         * provider.
         */
        if (!current_provider) {
            provider = ap_lookup_provider(AUTHN_PROVIDER_GROUP,
                                          AUTHN_DEFAULT_PROVIDER,
                                          AUTHN_PROVIDER_VERSION);

            if (!provider || !provider->check_password) {
                ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(01806)
                              "no authn provider configured");
                auth_result = AUTH_GENERAL_ERROR;
                break;
            }
            apr_table_setn(r->notes, AUTHN_PROVIDER_NAME_NOTE, AUTHN_DEFAULT_PROVIDER);
        }
        else {
            provider = current_provider->provider;
            apr_table_setn(r->notes, AUTHN_PROVIDER_NAME_NOTE, current_provider->provider_name);
        }

        if (!sent_user || !sent_pw) {
            auth_result = AUTH_USER_NOT_FOUND;
            break;
        }

        auth_result = provider->check_password(r, sent_user, sent_pw);

        apr_table_unset(r->notes, AUTHN_PROVIDER_NAME_NOTE);

        /* Something occurred. Stop checking. */
        if (auth_result != AUTH_USER_NOT_FOUND) {
            break;
        }

        /* If we're not really configured for providers, stop now. */
        if (!conf->providers) {
            break;
        }

        current_provider = current_provider->next;
    } while (current_provider);

    if (auth_result != AUTH_GRANTED) {
        int return_code;

        /* If we're not authoritative, then any error is ignored. */
        if (!(conf->authoritative) && auth_result != AUTH_DENIED) {
            return DECLINED;
        }

        switch (auth_result) {
        case AUTH_DENIED:
            ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(01807)
                          "user '%s': authentication failure for \"%s\": "
                          "password Mismatch",
                          sent_user, r->uri);
            return_code = HTTP_UNAUTHORIZED;
            break;
        case AUTH_USER_NOT_FOUND:
            ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(01808)
                          "user '%s' not found: %s", sent_user, r->uri);
            return_code = HTTP_UNAUTHORIZED;
            break;
        case AUTH_GENERAL_ERROR:
        default:
            /*
             * We'll assume that the module has already said what its error
             * was in the logs.
             */
            return_code = HTTP_INTERNAL_SERVER_ERROR;
            break;
        }

        /* If we're returning 401, tell them to try again. */
        if (return_code == HTTP_UNAUTHORIZED) {
            note_cookie_auth_failure(r);
        }

/* TODO: Flag the user somehow as to the reason for the failure */

        return return_code;
    }

    return OK;

}

/* fake the basic authentication header if configured to do so */
static void fake_basic_authentication(request_rec *r, auth_form_config_rec *conf,
                                      const char *user, const char *pw)
{
    if (conf->fakebasicauth) {
        char *basic = apr_pstrcat(r->pool, user, ":", pw, NULL);
        apr_size_t size = (apr_size_t) strlen(basic);
        char *base64 = apr_palloc(r->pool,
                                  apr_base64_encode_len(size + 1) * sizeof(char));
        apr_base64_encode(base64, basic, size);
        apr_table_setn(r->headers_in, "Authorization",
                       apr_pstrcat(r->pool, "Basic ", base64, NULL));
    }
}

/**
 * Must we use form authentication? If so, extract the cookie and run
 * the authnz hooks to determine if the login is valid.
 *
 * If the login is not valid, a 401 Not Authorized will be returned. It
 * is up to the webmaster to ensure this screen displays a suitable login
 * form to give the user the opportunity to log in.
 */
static int authenticate_form_authn(request_rec * r)
{
    auth_form_config_rec *conf = ap_get_module_config(r->per_dir_config,
                                                      &auth_form_module);
    const char *sent_user = NULL, *sent_pw = NULL, *sent_hash = NULL;
    const char *sent_loc = NULL, *sent_method = "GET", *sent_mimetype = NULL;
    const char *current_auth = NULL;
    const char *err;
    apr_status_t res;
    int rv = HTTP_UNAUTHORIZED;

    /* Are we configured to be Form auth? */
    current_auth = ap_auth_type(r);
    if (!current_auth || ap_cstr_casecmp(current_auth, "form")) {
        return DECLINED;
    }

    /*
     * XSS security warning: using cookies to store private data only works
     * when the administrator has full control over the source website. When
     * in forward-proxy mode, websites are public by definition, and so can
     * never be secure. Abort the auth attempt in this case.
     */
    if (PROXYREQ_PROXY == r->proxyreq) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(01809)
                      "form auth cannot be used for proxy "
                      "requests due to XSS risk, access denied: %s", r->uri);
        return HTTP_INTERNAL_SERVER_ERROR;
    }

    /* We need an authentication realm. */
    if (!ap_auth_name(r)) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(01810)
                      "need AuthName: %s", r->uri);
        return HTTP_INTERNAL_SERVER_ERROR;
    }

    r->ap_auth_type = (char *) current_auth;

    /* try get the username and password from the notes, if present */
    get_notes_auth(r, &sent_user, &sent_pw, &sent_method, &sent_mimetype);
    if (!sent_user || !sent_pw || !*sent_user || !*sent_pw) {

        /* otherwise try get the username and password from a session, if present */
        res = get_session_auth(r, &sent_user, &sent_pw, &sent_hash);

    }
    else {
        res = APR_SUCCESS;
    }

    /* first test whether the site passphrase matches */
    if (APR_SUCCESS == res && sent_user && sent_hash && sent_pw) {
        rv = check_site(r, conf->site, sent_user, sent_hash);
        if (OK == rv) {
            fake_basic_authentication(r, conf, sent_user, sent_pw);
            return OK;
        }
    }

    /* otherwise test for a normal password match */
    if (APR_SUCCESS == res && sent_user && sent_pw) {
        rv = check_authn(r, sent_user, sent_pw);
        if (OK == rv) {
            fake_basic_authentication(r, conf, sent_user, sent_pw);
            return OK;
        }
    }

    /*
     * If we reach this point, the request should fail with access denied,
     * except for one potential scenario:
     *
     * If the request is a POST, and the posted form contains user defined fields
     * for a username and a password, and the username and password are correct,
     * then return the response obtained by a GET to this URL.
     *
     * If an additional user defined location field is present in the form,
     * instead of a GET of the current URL, redirect the browser to the new
     * location.
     *
     * As a further option, if the user defined fields for the type of request,
     * the mime type of the body of the request, and the body of the request
     * itself are present, replace this request with a new request of the given
     * type and with the given body.
     *
     * Otherwise access is denied.
     *
     * Reading the body requires some song and dance, because the input filters
     * are not yet configured. To work around this problem, we create a
     * subrequest and use that to create a sane filter stack we can read the
     * form from.
     *
     * The main request is then capped with a kept_body input filter, which has
     * the effect of guaranteeing the input stack can be safely read a second time.
     *
     */
    if (HTTP_UNAUTHORIZED == rv && r->method_number == M_POST && ap_is_initial_req(r)) {
        request_rec *rr;
        apr_bucket_brigade *sent_body = NULL;

        /* create a subrequest of our current uri */
        rr = ap_sub_req_lookup_uri(r->uri, r, r->input_filters);
        rr->headers_in = r->headers_in;

        /* run the insert_filters hook on the subrequest to ensure a body read can
         * be done properly.
         */
        ap_run_insert_filter(rr);

        /* parse the form by reading the subrequest */
        rv = get_form_auth(rr, conf->username, conf->password, conf->location,
                           conf->method, conf->mimetype, conf->body,
                           &sent_user, &sent_pw, &sent_loc, &sent_method,
                           &sent_mimetype, &sent_body, conf);

        /* make sure any user detected within the subrequest is saved back to
         * the main request.
         */
        r->user = apr_pstrdup(r->pool, rr->user);

        /* we cannot clean up rr at this point, as memory allocated to rr is
         * referenced from the main request. It will be cleaned up when the
         * main request is cleaned up.
         */

        /* insert the kept_body filter on the main request to guarantee the
         * input filter stack cannot be read a second time, optionally inject
         * a saved body if one was specified in the login form.
         */
        if (sent_body && sent_mimetype) {
            apr_table_set(r->headers_in, "Content-Type", sent_mimetype);
            r->kept_body = sent_body;
        }
        else {
            r->kept_body = apr_brigade_create(r->pool, r->connection->bucket_alloc);
        }
        ap_request_insert_filter_fn(r);

        /* did the form ask to change the method? if so, switch in the redirect handler
         * to relaunch this request as the subrequest with the new method. If the
         * form didn't specify a method, the default value GET will force a redirect.
         */
        if (sent_method && strcmp(r->method, sent_method)) {
            r->handler = FORM_REDIRECT_HANDLER;
        }

        /* check the authn in the main request, based on the username found */
        if (OK == rv) {
            rv = check_authn(r, sent_user, sent_pw);
            if (OK == rv) {
                fake_basic_authentication(r, conf, sent_user, sent_pw);
                set_session_auth(r, sent_user, sent_pw, conf->site);
                if (sent_loc) {
                    apr_table_set(r->headers_out, "Location", sent_loc);
                    return HTTP_MOVED_TEMPORARILY;
                }
                if (conf->loginsuccess) {
                    const char *loginsuccess = ap_expr_str_exec(r,
                            conf->loginsuccess, &err);
                    if (!err) {
                        apr_table_set(r->headers_out, "Location", loginsuccess);
                        return HTTP_MOVED_TEMPORARILY;
                    }
                    else {
                        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(02339)
                                      "Can't evaluate login success expression: %s", err);
                        return HTTP_INTERNAL_SERVER_ERROR;
                    }
                }
            }
        }

    }

    /*
     * did the admin prefer to be redirected to the login page on failure
     * instead?
     */
    if (HTTP_UNAUTHORIZED == rv && conf->loginrequired) {
        const char *loginrequired = ap_expr_str_exec(r,
                conf->loginrequired, &err);
        if (!err) {
            apr_table_set(r->headers_out, "Location", loginrequired);
            return HTTP_MOVED_TEMPORARILY;
        }
        else {
            ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(02340)
                          "Can't evaluate login required expression: %s", err);
            return HTTP_INTERNAL_SERVER_ERROR;
        }
    }

    /* did the user ask to be redirected on login success? */
    if (sent_loc) {
        apr_table_set(r->headers_out, "Location", sent_loc);
        rv = HTTP_MOVED_TEMPORARILY;
    }


    /*
     * potential security issue: if we return a login to the browser, we must
     * send a no-store to make sure a well behaved browser will not try and
     * send the login details a second time if the back button is pressed.
     *
     * if the user has full control over the backend, the
     * AuthCookieDisableNoStore can be used to turn this off.
     */
    if (HTTP_UNAUTHORIZED == rv && !conf->disable_no_store) {
        apr_table_addn(r->headers_out, "Cache-Control", "no-store");
        apr_table_addn(r->err_headers_out, "Cache-Control", "no-store");
    }

    return rv;

}

/**
 * Handle a login attempt.
 *
 * If the login session is either missing or form authnz is unsuccessful, a
 * 401 Not Authorized will be returned to the browser. The webmaster
 * is expected to insert a login form into the 401 Not Authorized
 * error screen.
 *
 * If the webmaster wishes, they can point the form submission at this
 * handler, which will redirect the user to the correct page on success.
 * On failure, the 401 Not Authorized error screen will be redisplayed,
 * where the login attempt can be repeated.
 *
 */
static int authenticate_form_login_handler(request_rec * r)
{
    auth_form_config_rec *conf;
    const char *err;

    const char *sent_user = NULL, *sent_pw = NULL, *sent_loc = NULL;
    int rv;

    if (strcmp(r->handler, FORM_LOGIN_HANDLER)) {
        return DECLINED;
    }

    if (r->method_number != M_POST) {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(01811)
          "the " FORM_LOGIN_HANDLER " only supports the POST method for %s",
                      r->uri);
        return HTTP_METHOD_NOT_ALLOWED;
    }

    conf = ap_get_module_config(r->per_dir_config, &auth_form_module);

    rv = get_form_auth(r, conf->username, conf->password, conf->location,
                       NULL, NULL, NULL,
                       &sent_user, &sent_pw, &sent_loc,
                       NULL, NULL, NULL, conf);
    if (OK == rv) {
        rv = check_authn(r, sent_user, sent_pw);
        if (OK == rv) {
            set_session_auth(r, sent_user, sent_pw, conf->site);
            if (sent_loc) {
                apr_table_set(r->headers_out, "Location", sent_loc);
                return HTTP_MOVED_TEMPORARILY;
            }
            if (conf->loginsuccess) {
                const char *loginsuccess = ap_expr_str_exec(r,
                        conf->loginsuccess, &err);
                if (!err) {
                    apr_table_set(r->headers_out, "Location", loginsuccess);
                    return HTTP_MOVED_TEMPORARILY;
                }
                else {
                    ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(02341)
                                  "Can't evaluate login success expression: %s", err);
                    return HTTP_INTERNAL_SERVER_ERROR;
                }
            }
            return HTTP_OK;
        }
    }

    /* did we prefer to be redirected to the login page on failure instead? */
    if (HTTP_UNAUTHORIZED == rv && conf->loginrequired) {
        const char *loginrequired = ap_expr_str_exec(r,
                conf->loginrequired, &err);
        if (!err) {
            apr_table_set(r->headers_out, "Location", loginrequired);
            return HTTP_MOVED_TEMPORARILY;
        }
        else {
            ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(02342)
                          "Can't evaluate login required expression: %s", err);
            return HTTP_INTERNAL_SERVER_ERROR;
        }
    }

    return rv;

}

/**
 * Handle a logout attempt.
 *
 * If an attempt is made to access this URL, any username and password
 * embedded in the session is deleted.
 *
 * This has the effect of logging the person out.
 *
 * If a logout URI has been specified, this function will create an
 * internal redirect to this page.
 */
static int authenticate_form_logout_handler(request_rec * r)
{
    auth_form_config_rec *conf;
    const char *err;

    if (strcmp(r->handler, FORM_LOGOUT_HANDLER)) {
        return DECLINED;
    }

    conf = ap_get_module_config(r->per_dir_config, &auth_form_module);

    /* remove the username and password, effectively logging the user out */
    set_session_auth(r, NULL, NULL, NULL);

    /*
     * make sure the logout page is never cached - otherwise the logout won't
     * work!
     */
    apr_table_addn(r->headers_out, "Cache-Control", "no-store");
    apr_table_addn(r->err_headers_out, "Cache-Control", "no-store");

    /* if set, internal redirect to the logout page */
    if (conf->logout) {
        const char *logout = ap_expr_str_exec(r,
                conf->logout, &err);
        if (!err) {
            apr_table_addn(r->headers_out, "Location", logout);
            return HTTP_TEMPORARY_REDIRECT;
        }
        else {
            ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(02343)
                          "Can't evaluate logout expression: %s", err);
            return HTTP_INTERNAL_SERVER_ERROR;
        }
    }

    return HTTP_OK;

}

/**
 * Handle a redirect attempt.
 *
 * If during a form login, the method, mimetype and request body are
 * specified, this handler will ensure that this request is included
 * as an internal redirect.
 *
 */
static int authenticate_form_redirect_handler(request_rec * r)
{

    request_rec *rr = NULL;
    const char *sent_method = NULL, *sent_mimetype = NULL;

    if (strcmp(r->handler, FORM_REDIRECT_HANDLER)) {
        return DECLINED;
    }

    /* get the method and mimetype from the notes */
    get_notes_auth(r, NULL, NULL, &sent_method, &sent_mimetype);

    if (r->kept_body && sent_method && sent_mimetype) {

        ap_log_rerror(APLOG_MARK, APLOG_DEBUG, 0, r, APLOGNO(01812)
          "internal redirect to method '%s' and body mimetype '%s' for the "
                      "uri: %s", sent_method, sent_mimetype, r->uri);

        rr = ap_sub_req_method_uri(sent_method, r->uri, r, r->output_filters);
        r->status = ap_run_sub_req(rr);

    }
    else {
        ap_log_rerror(APLOG_MARK, APLOG_ERR, 0, r, APLOGNO(01813)
        "internal redirect requested but one or all of method, mimetype or "
                      "body are NULL: %s", r->uri);
        return HTTP_INTERNAL_SERVER_ERROR;
    }

    /* return the underlying error, or OK on success */
    return r->status == HTTP_OK || r->status == OK ? OK : r->status;

}

static int authenticate_form_post_config(apr_pool_t *pconf, apr_pool_t *plog,
        apr_pool_t *ptemp, server_rec *s)
{

    if (!ap_session_load_fn || !ap_session_get_fn || !ap_session_set_fn) {
        ap_session_load_fn = APR_RETRIEVE_OPTIONAL_FN(ap_session_load);
        ap_session_get_fn = APR_RETRIEVE_OPTIONAL_FN(ap_session_get);
        ap_session_set_fn = APR_RETRIEVE_OPTIONAL_FN(ap_session_set);
        if (!ap_session_load_fn || !ap_session_get_fn || !ap_session_set_fn) {
            ap_log_error(APLOG_MARK, APLOG_CRIT, 0, NULL, APLOGNO(02617)
                    "You must load mod_session to enable the mod_auth_form "
                                       "functions");
            return !OK;
        }
    }

    if (!ap_request_insert_filter_fn || !ap_request_remove_filter_fn) {
        ap_request_insert_filter_fn = APR_RETRIEVE_OPTIONAL_FN(ap_request_insert_filter);
        ap_request_remove_filter_fn = APR_RETRIEVE_OPTIONAL_FN(ap_request_remove_filter);
        if (!ap_request_insert_filter_fn || !ap_request_remove_filter_fn) {
            ap_log_error(APLOG_MARK, APLOG_CRIT, 0, NULL, APLOGNO(02618)
                    "You must load mod_request to enable the mod_auth_form "
                                       "functions");
            return !OK;
        }
    }

    return OK;
}

static void register_hooks(apr_pool_t * p)
{
    ap_hook_post_config(authenticate_form_post_config,NULL,NULL,APR_HOOK_MIDDLE);

#if AP_MODULE_MAGIC_AT_LEAST(20080403,1)
    ap_hook_check_authn(authenticate_form_authn, NULL, NULL, APR_HOOK_MIDDLE,
                        AP_AUTH_INTERNAL_PER_CONF);
#else
    ap_hook_check_user_id(authenticate_form_authn, NULL, NULL, APR_HOOK_MIDDLE);
#endif
    ap_hook_handler(authenticate_form_login_handler, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_handler(authenticate_form_logout_handler, NULL, NULL, APR_HOOK_MIDDLE);
    ap_hook_handler(authenticate_form_redirect_handler, NULL, NULL, APR_HOOK_MIDDLE);

    ap_hook_note_auth_failure(hook_note_cookie_auth_failure, NULL, NULL,
                              APR_HOOK_MIDDLE);
}

AP_DECLARE_MODULE(auth_form) =
{
    STANDARD20_MODULE_STUFF,
    create_auth_form_dir_config, /* dir config creater */
    merge_auth_form_dir_config,  /* dir merger --- default is to override */
    NULL,                        /* server config */
    NULL,                        /* merge server config */
    auth_form_cmds,              /* command apr_table_t */
    register_hooks               /* register hooks */
};
