Source/WebCore/loader/PrivateClickMeasurement.cpp

/*
 * Copyright (C) 2019 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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#include "config.h"
#include "PrivateClickMeasurement.h"

#include "Logging.h"
#include "RuntimeEnabledFeatures.h"
#include <wtf/CrossThreadCopier.h>
#include <wtf/Expected.h>
#include <wtf/RandomNumber.h>
#include <wtf/URL.h>
#include <wtf/text/StringConcatenateNumbers.h>
#include <wtf/text/StringToIntegerConversion.h>
#include <wtf/text/StringView.h>

namespace WebCore {

static constexpr auto privateClickMeasurementTriggerAttributionPath = "/.well-known/private-click-measurement/trigger-attribution/"_s;
static const char privateClickMeasurementTokenSignaturePath[] = "/.well-known/private-click-measurement/sign-unlinkable-token/";
static const char privateClickMeasurementTokenPublicKeyPath[] = "/.well-known/private-click-measurement/get-token-public-key/";
static const char privateClickMeasurementReportAttributionPath[] = "/.well-known/private-click-measurement/report-attribution/";
static constexpr auto privateClickMeasurementToSKAdNetworkURLPrefix = "https://apps.apple.com/app/apple-store/id"_s;
const size_t privateClickMeasurementAttributionTriggerDataPathSegmentSize = 2;
const size_t privateClickMeasurementPriorityPathSegmentSize = 2;
const uint8_t privateClickMeasurementVersion = 3;

const Seconds PrivateClickMeasurement::maxAge()
{
    return 24_h * 7;
};

bool PrivateClickMeasurement::isValid() const
{
    return m_attributionTriggerData
        && m_attributionTriggerData.value().isValid()
        && !m_sourceSite.registrableDomain.isEmpty()
        && !m_destinationSite.registrableDomain.isEmpty()
        && (m_timesToSend.sourceEarliestTimeToSend || m_timesToSend.destinationEarliestTimeToSend);
}

PrivateClickMeasurement::UnlinkableToken PrivateClickMeasurement::UnlinkableToken::isolatedCopy() const &
{
    return {
#if PLATFORM(COCOA)
        blinder, waitingToken, readyToken,
#endif
        valueBase64URL.isolatedCopy()
    };
}

PrivateClickMeasurement::UnlinkableToken PrivateClickMeasurement::UnlinkableToken::isolatedCopy() &&
{
    return {
#if PLATFORM(COCOA)
        blinder, waitingToken, readyToken,
#endif
        WTFMove(valueBase64URL).isolatedCopy()
    };
}

PrivateClickMeasurement PrivateClickMeasurement::isolatedCopy() const &
{
    PrivateClickMeasurement copy {
        m_sourceID,
        m_sourceSite.isolatedCopy(),
        m_destinationSite.isolatedCopy(),
        m_sourceApplicationBundleID.isolatedCopy(),
        m_timeOfAdClick.isolatedCopy(),
        m_isEphemeral,
    };
    copy.m_attributionTriggerData = m_attributionTriggerData;
    copy.m_timesToSend = m_timesToSend;
    copy.m_ephemeralSourceNonce = crossThreadCopy(m_ephemeralSourceNonce);
    copy.m_sourceUnlinkableToken = m_sourceUnlinkableToken.isolatedCopy();
    copy.m_sourceSecretToken = crossThreadCopy(m_sourceSecretToken);
    return copy;
}

PrivateClickMeasurement PrivateClickMeasurement::isolatedCopy() &&
{
    PrivateClickMeasurement copy {
        m_sourceID,
        WTFMove(m_sourceSite).isolatedCopy(),
        WTFMove(m_destinationSite).isolatedCopy(),
        WTFMove(m_sourceApplicationBundleID).isolatedCopy(),
        WTFMove(m_timeOfAdClick).isolatedCopy(),
        m_isEphemeral,
    };
    copy.m_attributionTriggerData = WTFMove(m_attributionTriggerData);
    copy.m_timesToSend = WTFMove(m_timesToSend);
    copy.m_ephemeralSourceNonce = crossThreadCopy(WTFMove(m_ephemeralSourceNonce));
    copy.m_sourceUnlinkableToken = WTFMove(m_sourceUnlinkableToken).isolatedCopy();
    copy.m_sourceSecretToken = crossThreadCopy(WTFMove(m_sourceSecretToken));
    return copy;
}

bool PrivateClickMeasurement::isNeitherSameSiteNorCrossSiteTriggeringEvent(const RegistrableDomain& redirectDomain, const URL& firstPartyURL, const AttributionTriggerData& attributionTriggerData)
{
    auto isSameSiteTriggeringEvent = redirectDomain.matches(firstPartyURL) && attributionTriggerData.sourceRegistrableDomain;
    if (isSameSiteTriggeringEvent)
        return false;
    auto isCrossSiteTriggeringEvent = sourceSite().registrableDomain == redirectDomain && !attributionTriggerData.sourceRegistrableDomain;
    return !isCrossSiteTriggeringEvent;
}

Expected<PrivateClickMeasurement::AttributionTriggerData, String> PrivateClickMeasurement::parseAttributionRequestQuery(const URL& redirectURL)
{
    if (!redirectURL.hasQuery())
        return AttributionTriggerData { };

    auto parameters = queryParameters(redirectURL);
    if (!parameters.size())
        return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL had a query string but it didn't contain supported parameters."_s);

    if (parameters.size() > 2)
        return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's query string contained unsupported parameters."_s);

    EphemeralNonce destinationNonce;
    RegistrableDomain sourceDomain;
    for (auto& parameter : parameters) {
        if (parameter.key == "attributionSource"_s) {
            if (parameter.value.isEmpty())
                return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's attributionSource query parameter had no value."_s);
            if (!sourceDomain.isEmpty())
                return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL had multiple attributionSource query parameters."_s);

            URL attributionSourceURL { parameter.value };
            if (!attributionSourceURL.isValid() || (attributionSourceURL.hasPath() && attributionSourceURL.path().length() > 1) || attributionSourceURL.hasCredentials() || attributionSourceURL.hasQuery() || attributionSourceURL.hasFragmentIdentifier())
                return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's attributionSource query parameter was not a valid URL or was a URL with a path, credentials, query string, or fragment."_s);
            sourceDomain = RegistrableDomain { attributionSourceURL };

            if (sourceDomain.isEmpty())
                return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's attributionSource query parameter had no registrable domain."_s);
        } else if (parameter.key == "attributionDestinationNonce"_s) {
            if (parameter.value.isEmpty())
                return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's attributionDestinationNonce query parameter had no value."_s);
            if (!destinationNonce.nonce.isEmpty())
                return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL had multiple attributionDestinationNonce query parameters."_s);

            destinationNonce.nonce = parameter.value;
        } else
            return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's query string contained unsupported parameters."_s);
    }

    AttributionTriggerData attributionTriggerData;
    if (!sourceDomain.isEmpty())
        attributionTriggerData.sourceRegistrableDomain = WTFMove(sourceDomain);

    if (!destinationNonce.nonce.isEmpty())
        attributionTriggerData.ephemeralDestinationNonce = WTFMove(destinationNonce);

    return attributionTriggerData;
}

Expected<PrivateClickMeasurement::AttributionTriggerData, String> PrivateClickMeasurement::parseAttributionRequest(const URL& redirectURL)
{
    auto path = StringView(redirectURL.string()).substring(redirectURL.pathStart(), redirectURL.pathEnd() - redirectURL.pathStart());
    if (path.isEmpty() || !path.startsWith(privateClickMeasurementTriggerAttributionPath))
        return makeUnexpected(nullString());

    if (!redirectURL.protocolIs("https"_s) || redirectURL.hasCredentials() || redirectURL.hasFragmentIdentifier())
        return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's protocol is not HTTPS or the URL contains one or more of username, password, and fragment."_s);

    auto result = parseAttributionRequestQuery(redirectURL);
    if (!result) {
        if (!result.error().isEmpty())
            return result;
        return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL's query string could not be parsed."_s);
    }
    auto attributionTriggerData = result.value();

    auto prefixLength = privateClickMeasurementTriggerAttributionPath.length();
    if (path.length() == prefixLength + privateClickMeasurementAttributionTriggerDataPathSegmentSize) {
        auto attributionTriggerDataUInt64 = parseInteger<uint64_t>(path.substring(prefixLength, privateClickMeasurementAttributionTriggerDataPathSegmentSize));
        if (!attributionTriggerDataUInt64 || *attributionTriggerDataUInt64 > AttributionTriggerData::MaxEntropy)
            return makeUnexpected(makeString("[Private Click Measurement] Triggering event was not accepted because the conversion data could not be parsed or was higher than the allowed maximum of "_s, AttributionTriggerData::MaxEntropy, "."_s));

        attributionTriggerData.data = static_cast<uint8_t>(*attributionTriggerDataUInt64);
        attributionTriggerData.priority = 0;
        return attributionTriggerData;
    }
    
    if (path.length() == prefixLength + privateClickMeasurementAttributionTriggerDataPathSegmentSize + 1 + privateClickMeasurementPriorityPathSegmentSize) {
        auto attributionTriggerDataUInt64 = parseInteger<uint64_t>(path.substring(prefixLength, privateClickMeasurementAttributionTriggerDataPathSegmentSize));
        if (!attributionTriggerDataUInt64 || *attributionTriggerDataUInt64 > AttributionTriggerData::MaxEntropy)
            return makeUnexpected(makeString("[Private Click Measurement] Triggering event was not accepted because the conversion data could not be parsed or was higher than the allowed maximum of "_s, AttributionTriggerData::MaxEntropy, "."_s));

        auto attributionPriorityUInt64 = parseInteger<uint64_t>(path.substring(prefixLength + privateClickMeasurementAttributionTriggerDataPathSegmentSize + 1, privateClickMeasurementPriorityPathSegmentSize));
        if (!attributionPriorityUInt64 || *attributionPriorityUInt64 > Priority::MaxEntropy)
            return makeUnexpected(makeString("[Private Click Measurement] Triggering event was not accepted because the priority could not be parsed or was higher than the allowed maximum of "_s, Priority::MaxEntropy, "."_s));

        attributionTriggerData.data = static_cast<uint8_t>(*attributionTriggerDataUInt64);
        attributionTriggerData.priority = static_cast<uint8_t>(*attributionPriorityUInt64);
        return attributionTriggerData;
    }

    return makeUnexpected("[Private Click Measurement] Triggering event was not accepted because the URL path contained unrecognized parts."_s);
}

bool PrivateClickMeasurement::hasPreviouslyBeenReported()
{
    return !m_timesToSend.sourceEarliestTimeToSend || !m_timesToSend.destinationEarliestTimeToSend;
}

void PrivateClickMeasurement::setSourceApplicationBundleIDForTesting(const String& appBundleIDForTesting)
{
    m_sourceApplicationBundleID = appBundleIDForTesting;
}

static Seconds randomlyBetweenTwentyFourAndFortyEightHours(PrivateClickMeasurement::IsRunningLayoutTest isRunningTest)
{
    return isRunningTest == PrivateClickMeasurement::IsRunningLayoutTest::Yes ? 1_s : 24_h + Seconds(randomNumber() * (24_h).value());
}

PrivateClickMeasurement::AttributionSecondsUntilSendData PrivateClickMeasurement::attributeAndGetEarliestTimeToSend(AttributionTriggerData&& attributionTriggerData, IsRunningLayoutTest isRunningTest)
{
    if (!attributionTriggerData.isValid() || (m_attributionTriggerData && m_attributionTriggerData->priority >= attributionTriggerData.priority))
        return { };

    m_attributionTriggerData = WTFMove(attributionTriggerData);
    // 24-48 hour delay before sending. This helps privacy since the conversion and the attribution
    // requests are detached and the time of the attribution does not reveal the time of the conversion.
    auto sourceSecondsUntilSend = randomlyBetweenTwentyFourAndFortyEightHours(isRunningTest);
    auto destinationSecondsUntilSend = randomlyBetweenTwentyFourAndFortyEightHours(isRunningTest);
    m_timesToSend = { WallTime::now() + sourceSecondsUntilSend, WallTime::now() + destinationSecondsUntilSend };

    return AttributionSecondsUntilSendData { sourceSecondsUntilSend, destinationSecondsUntilSend };
}

bool PrivateClickMeasurement::hasHigherPriorityThan(const PrivateClickMeasurement& other) const
{
    if (!other.m_attributionTriggerData)
        return true;
    
    if (!m_attributionTriggerData)
        return false;

    return m_attributionTriggerData->priority > other.m_attributionTriggerData->priority;
}

static URL makeValidURL(const RegistrableDomain& domain, const char* path)
{
    URL validURL { makeString("https://", domain.string(), path) };
    return validURL.isValid() ? validURL : URL { };
}

static URL attributionReportURL(const RegistrableDomain& domain)
{
    return makeValidURL(domain, privateClickMeasurementReportAttributionPath);
}

URL PrivateClickMeasurement::attributionReportClickSourceURL() const
{
    if (!isValid())
        return URL();

    return attributionReportURL(m_sourceSite.registrableDomain);
}

URL PrivateClickMeasurement::attributionReportClickDestinationURL() const
{
    if (!isValid())
        return URL();

    return attributionReportURL(m_destinationSite.registrableDomain);
}

Ref<JSON::Object> PrivateClickMeasurement::attributionReportJSON() const
{
    auto reportDetails = JSON::Object::create();
    if (!m_attributionTriggerData || !isValid())
        return reportDetails;

    reportDetails->setString("source_engagement_type"_s, "click"_s);
    reportDetails->setString("source_site"_s, m_sourceSite.registrableDomain.string());
    reportDetails->setInteger("source_id"_s, m_sourceID.id);
    reportDetails->setString("attributed_on_site"_s, m_destinationSite.registrableDomain.string());
    reportDetails->setInteger("trigger_data"_s, m_attributionTriggerData->data);
    reportDetails->setInteger("version"_s, privateClickMeasurementVersion);

    // This token has been kept secret this far and cannot be linked to the unlinkable token.
    if (m_sourceSecretToken) {
        reportDetails->setString("source_secret_token"_s, m_sourceSecretToken->tokenBase64URL);
        reportDetails->setString("source_secret_token_signature"_s, m_sourceSecretToken->signatureBase64URL);
    }

    // This token has been kept secret this far and cannot be linked to the unlinkable token.
    if (m_attributionTriggerData->destinationSecretToken) {
        reportDetails->setString("destination_secret_token"_s, m_attributionTriggerData->destinationSecretToken->tokenBase64URL);
        reportDetails->setString("destination_secret_token_signature"_s, m_attributionTriggerData->destinationSecretToken->signatureBase64URL);
    }

    return reportDetails;
}

// MARK: - Fraud Prevention

static constexpr uint32_t EphemeralNonceRequiredNumberOfBytes = 16;

bool PrivateClickMeasurement::EphemeralNonce::isValid() const
{
    // FIXME: Investigate if we can do with a simple length check instead of decoding.
    // https://bugs.webkit.org/show_bug.cgi?id=221945
    auto digest = base64URLDecode(nonce);
    if (!digest)
        return false;
    return digest->size() == EphemeralNonceRequiredNumberOfBytes;
}

void PrivateClickMeasurement::setEphemeralSourceNonce(EphemeralNonce&& nonce)
{
    if (!nonce.isValid())
        return;
    m_ephemeralSourceNonce = WTFMove(nonce);
}

const std::optional<const URL> PrivateClickMeasurement::tokenPublicKeyURL(const RegistrableDomain& registrableDomain)
{
    if (registrableDomain.isEmpty())
        return std::nullopt;
    return makeValidURL(registrableDomain, privateClickMeasurementTokenPublicKeyPath);
}

const std::optional<const URL> PrivateClickMeasurement::tokenPublicKeyURL() const
{
    return tokenPublicKeyURL(m_sourceSite.registrableDomain);
}

const std::optional<const URL> PrivateClickMeasurement::tokenSignatureURL(const RegistrableDomain& registrableDomain)
{
    if (registrableDomain.isEmpty())
        return std::nullopt;
    return makeValidURL(registrableDomain, privateClickMeasurementTokenSignaturePath);
}

const std::optional<const URL> PrivateClickMeasurement::tokenSignatureURL() const
{
    if (!m_ephemeralSourceNonce || !m_ephemeralSourceNonce->isValid())
        return std::nullopt;

    return tokenSignatureURL(m_sourceSite.registrableDomain);
}

Ref<JSON::Object> PrivateClickMeasurement::tokenSignatureJSON() const
{
    auto reportDetails = JSON::Object::create();
    if (!m_ephemeralSourceNonce || !m_ephemeralSourceNonce->isValid())
        return reportDetails;

    if (m_sourceUnlinkableToken.valueBase64URL.isEmpty())
        return reportDetails;

    reportDetails->setString("source_engagement_type"_s, "click"_s);
    reportDetails->setString("source_nonce"_s, m_ephemeralSourceNonce->nonce);
    // This token can not be linked to the secret token.
    reportDetails->setString("source_unlinkable_token"_s, m_sourceUnlinkableToken.valueBase64URL);
    reportDetails->setInteger("version"_s, privateClickMeasurementVersion);
    return reportDetails;
}

Ref<JSON::Object> PrivateClickMeasurement::AttributionTriggerData::tokenSignatureJSON() const
{
    auto reportDetails = JSON::Object::create();
    if (!ephemeralDestinationNonce || !ephemeralDestinationNonce->isValid())
        return reportDetails;

    if (!destinationUnlinkableToken || destinationUnlinkableToken->valueBase64URL.isEmpty())
        return reportDetails;

    reportDetails->setString("source_engagement_type"_s, "click"_s);
    reportDetails->setString("destination_nonce"_s, ephemeralDestinationNonce->nonce);
    // This token can not be linked to the secret token.
    reportDetails->setString("destination_unlinkable_token"_s, destinationUnlinkableToken->valueBase64URL);
    reportDetails->setInteger("version"_s, privateClickMeasurementVersion);
    return reportDetails;
}

bool PrivateClickMeasurement::SecretToken::isValid() const
{
    return !(tokenBase64URL.isEmpty() || signatureBase64URL.isEmpty() || keyIDBase64URL.isEmpty());
}

void PrivateClickMeasurement::setSourceSecretToken(SourceSecretToken&& token)
{
    if (!token.isValid())
        return;
    m_sourceSecretToken = WTFMove(token);
}

void PrivateClickMeasurement::setDestinationSecretToken(DestinationSecretToken&& token)
{
    if (!token.isValid() || !m_attributionTriggerData)
        return;
    m_attributionTriggerData->destinationSecretToken = WTFMove(token);
}

std::optional<uint64_t> PrivateClickMeasurement::appStoreURLAdamID(const URL& url)
{
    StringView stringView { url.string() };
    if (!stringView.startsWith(privateClickMeasurementToSKAdNetworkURLPrefix))
        return std::nullopt;
    return parseInteger<uint64_t>(stringView.substring(privateClickMeasurementToSKAdNetworkURLPrefix.length()));
}

} // namespace WebCore