/*    Copyright 2012 10gen Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects
 *    for all of the code used other than as permitted herein. If you modify
 *    file(s) with this exception, you may extend this exception to your
 *    version of the file(s), but you are not obligated to do so. If you do not
 *    wish to do so, delete this exception statement from your version. If you
 *    delete this exception statement from all source files in the program,
 *    then also delete it in the license file.
 */

/**
 * This module implements the client side of SASL authentication in MongoDB, in terms of the Cyrus
 * SASL library.  See <sasl/sasl.h> and http://cyrusimap.web.cmu.edu/ for relevant documentation.
 *
 * The primary entry point at runtime is saslClientAuthenticateImpl().
 */

#define MONGO_LOG_DEFAULT_COMPONENT ::mongo::logger::LogComponent::kNetwork

#include "mongo/platform/basic.h"

#include <cstdint>
#include <string>

#include "mongo/base/init.h"
#include "mongo/base/status.h"
#include "mongo/base/string_data.h"
#include "mongo/bson/util/bson_extract.h"
#include "mongo/client/sasl_client_authenticate.h"
#include "mongo/client/sasl_client_session.h"
#include "mongo/rpc/get_status_from_command_result.h"
#include "mongo/util/base64.h"
#include "mongo/util/log.h"
#include "mongo/util/net/hostandport.h"
#include "mongo/util/password_digest.h"

namespace mongo {

using std::endl;
using executor::RemoteCommandRequest;
using executor::RemoteCommandResponse;

namespace {

// Default log level on the client for SASL log messages.
const int defaultSaslClientLogLevel = 4;

const char* const saslClientLogFieldName = "clientLogLevel";

int getSaslClientLogLevel(const BSONObj& saslParameters) {
    int saslLogLevel = defaultSaslClientLogLevel;
    BSONElement saslLogElement = saslParameters[saslClientLogFieldName];
    if (saslLogElement.trueValue())
        saslLogLevel = 1;
    if (saslLogElement.isNumber())
        saslLogLevel = saslLogElement.numberInt();
    return saslLogLevel;
}

/**
 * Gets the password data from "saslParameters" and stores it to "outPassword".
 *
 * If "digestPassword" indicates that the password needs to be "digested" via
 * mongo::createPasswordDigest(), this method takes care of that.
 * On success, the value of "*outPassword" is always the correct value to set
 * as the password on the SaslClientSession.
 *
 * Returns Status::OK() on success, and ErrorCodes::NoSuchKey if the password data is not
 * present in "saslParameters".  Other ErrorCodes returned indicate other errors.
 */
Status extractPassword(const BSONObj& saslParameters,
                       bool digestPassword,
                       std::string* outPassword) {
    std::string rawPassword;
    Status status =
        bsonExtractStringField(saslParameters, saslCommandPasswordFieldName, &rawPassword);
    if (!status.isOK())
        return status;

    if (digestPassword) {
        std::string user;
        status = bsonExtractStringField(saslParameters, saslCommandUserFieldName, &user);
        if (!status.isOK())
            return status;

        *outPassword = mongo::createPasswordDigest(user, rawPassword);
    } else {
        *outPassword = rawPassword;
    }
    return Status::OK();
}

/**
 * Configures "session" to perform the client side of a SASL conversation over connection
 * "client".
 *
 * "saslParameters" is a BSON document providing the necessary configuration information.
 *
 * Returns Status::OK() on success.
 */
Status configureSession(SaslClientSession* session,
                        StringData hostname,
                        StringData targetDatabase,
                        const BSONObj& saslParameters) {
    std::string mechanism;
    Status status =
        bsonExtractStringField(saslParameters, saslCommandMechanismFieldName, &mechanism);
    if (!status.isOK())
        return status;
    session->setParameter(SaslClientSession::parameterMechanism, mechanism);

    std::string value;
    status = bsonExtractStringFieldWithDefault(
        saslParameters, saslCommandServiceNameFieldName, saslDefaultServiceName, &value);
    if (!status.isOK())
        return status;
    session->setParameter(SaslClientSession::parameterServiceName, value);

    status = bsonExtractStringFieldWithDefault(
        saslParameters, saslCommandServiceHostnameFieldName, hostname, &value);
    if (!status.isOK())
        return status;
    session->setParameter(SaslClientSession::parameterServiceHostname, value);

    status = bsonExtractStringField(saslParameters, saslCommandUserFieldName, &value);
    if (!status.isOK())
        return status;
    session->setParameter(SaslClientSession::parameterUser, value);

    bool digestPasswordDefault = !(targetDatabase == "$external" && mechanism == "PLAIN") &&
        !(targetDatabase == "$external" && mechanism == "GSSAPI");
    bool digestPassword;
    status = bsonExtractBooleanFieldWithDefault(
        saslParameters, saslCommandDigestPasswordFieldName, digestPasswordDefault, &digestPassword);
    if (!status.isOK())
        return status;

    status = extractPassword(saslParameters, digestPassword, &value);
    if (status.isOK()) {
        session->setParameter(SaslClientSession::parameterPassword, value);
    } else if (!(status == ErrorCodes::NoSuchKey && targetDatabase == "$external")) {
        // $external users do not have passwords, hence NoSuchKey is expected
        return status;
    }

    return session->initialize();
}

void asyncSaslConversation(auth::RunCommandHook runCommand,
                           const std::shared_ptr<SaslClientSession>& session,
                           const BSONObj& saslCommandPrefix,
                           const BSONObj& inputObj,
                           StringData targetDatabase,
                           int saslLogLevel,
                           auth::AuthCompletionHandler handler) {
    // Extract payload from previous step
    std::string payload;
    BSONType type;
    auto status = saslExtractPayload(inputObj, &payload, &type);
    if (!status.isOK())
        return handler(std::move(status));

    LOG(saslLogLevel) << "sasl client input: " << base64::encode(payload) << endl;

    // Create new payload for our response
    std::string responsePayload;
    status = session->step(payload, &responsePayload);
    if (!status.isOK())
        return handler(std::move(status));

    LOG(saslLogLevel) << "sasl client output: " << base64::encode(responsePayload) << endl;

    // Build command using our new payload and conversationId
    BSONObjBuilder commandBuilder;
    commandBuilder.appendElements(saslCommandPrefix);
    commandBuilder.appendBinData(saslCommandPayloadFieldName,
                                 int(responsePayload.size()),
                                 BinDataGeneral,
                                 responsePayload.c_str());
    BSONElement conversationId = inputObj[saslCommandConversationIdFieldName];
    if (!conversationId.eoo())
        commandBuilder.append(conversationId);

    auto request = RemoteCommandRequest();
    request.dbname = targetDatabase.toString();
    request.cmdObj = commandBuilder.obj();

    // Asynchronously continue the conversation
    runCommand(
        request,
        [runCommand, session, targetDatabase, saslLogLevel, handler](auth::AuthResponse response) {
            if (!response.isOK()) {
                return handler(std::move(response));
            }

            auto serverResponse = response.getValue().data.getOwned();
            auto code = getStatusFromCommandResult(serverResponse).code();

            // Server versions 2.3.2 and earlier may return "ok: 1" with a non-zero
            // "code" field, indicating a failure.  Subsequent versions should
            // return "ok: 0" on failure with a non-zero "code" field to indicate specific
            // failure. In all versions, either (ok: 1, code: > 0) or (ok: 0, code optional)
            // indicate failure.
            if (code != ErrorCodes::OK) {
                return handler({code, serverResponse[saslCommandErrmsgFieldName].str()});
            }

            // Exit if we have finished
            if (session->isDone()) {
                bool isServerDone = serverResponse[saslCommandDoneFieldName].trueValue();
                if (!isServerDone) {
                    return handler({ErrorCodes::ProtocolError, "Client finished before server."});
                }
                return handler(std::move(response));
            }

            BSONObj saslFollowupCommandPrefix = BSON(saslContinueCommandName << 1);
            asyncSaslConversation(runCommand,
                                  session,
                                  std::move(saslFollowupCommandPrefix),
                                  std::move(serverResponse),
                                  targetDatabase,
                                  saslLogLevel,
                                  handler);
        });
}

/**
 * Driver for the client side of a sasl authentication session, conducted synchronously over
 * "client".
 */
void saslClientAuthenticateImpl(auth::RunCommandHook runCommand,
                                StringData hostname,
                                const BSONObj& saslParameters,
                                auth::AuthCompletionHandler handler) {
    int saslLogLevel = getSaslClientLogLevel(saslParameters);
    std::string targetDatabase;
    try {
        Status status = bsonExtractStringFieldWithDefault(
            saslParameters, saslCommandUserDBFieldName, saslDefaultDBName, &targetDatabase);
        if (!status.isOK())
            return handler(std::move(status));
    } catch (const DBException& ex) {
        return handler(ex.toStatus());
    }

    std::string mechanism;
    Status status =
        bsonExtractStringField(saslParameters, saslCommandMechanismFieldName, &mechanism);
    if (!status.isOK()) {
        return handler(std::move(status));
    }

    // NOTE: this must be a shared_ptr so that we can capture it in a lambda later on.
    // Come C++14, we should be able to do this in a nicer way.
    std::shared_ptr<SaslClientSession> session(SaslClientSession::create(mechanism));

    status = configureSession(session.get(), hostname, targetDatabase, saslParameters);
    if (!status.isOK())
        return handler(std::move(status));

    BSONObj saslFirstCommandPrefix =
        BSON(saslStartCommandName << 1 << saslCommandMechanismFieldName
                                  << session->getParameter(SaslClientSession::parameterMechanism));
    BSONObj inputObj = BSON(saslCommandPayloadFieldName << "");
    asyncSaslConversation(runCommand,
                          session,
                          std::move(saslFirstCommandPrefix),
                          std::move(inputObj),
                          targetDatabase,
                          saslLogLevel,
                          handler);
}

MONGO_INITIALIZER(SaslClientAuthenticateFunction)(InitializerContext* context) {
    saslClientAuthenticate = saslClientAuthenticateImpl;
    return Status::OK();
}

}  // namespace
}  // namespace mongo