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// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "chrome/browser/webauthn/challenge_url_fetcher.h"
#include "base/functional/bind.h"
#include "components/device_event_log/device_event_log.h"
#include "net/http/http_response_headers.h"
#include "net/http/http_response_info.h"
#include "net/http/http_status_code.h"
#include "net/traffic_annotation/network_traffic_annotation.h"
#include "services/network/public/cpp/resource_request.h"
#include "services/network/public/cpp/shared_url_loader_factory.h"
#include "services/network/public/cpp/simple_url_loader.h"
#include "services/network/public/mojom/fetch_api.mojom.h"
#include "services/network/public/mojom/url_response_head.mojom.h"
namespace {
// The specification says a challenge must be at least 16 bytes but does not
// provide an upper bound. 1KiB should contain any reasonable challenge.
const size_t kMaxChallengeSize = 1024;
const size_t kMinChallengeSize = 16;
constexpr char kChallengeContentType[] = "application/x-webauthn-challenge";
const net::NetworkTrafficAnnotationTag kTrafficAnnotation =
net::DefineNetworkTrafficAnnotation("webauthn_challenge_fetch", R"(
semantics {
sender: "Web Authentication Client"
description:
"When a user attempts to sign in to a site using a WebAuthn "
"credential, the site can include a challenge in the request, or "
"else a URL from which the challenge can be asynchronously "
"fetched. A challenge is a random byte string that protects "
"against replay attacks. This request is the challenge request "
"to the provided URL."
trigger:
"A user attempts a Web Authentication sign-in on a web site."
data:
"In response to this HTTP GET, the site returns a random string "
"of bytes that will be signed over and embedded in the response "
"to the WebAuthn request, if that request is successful."
internal {
contacts {
email: "chrome-webauthn@google.com"
}
}
user_data {
type: NONE
}
destination: WEBSITE
last_reviewed: "2024-12-03"
}
policy {
cookies_allowed: NO
setting: "This cannot be disabled."
policy_exception_justification:
"This request is part of a web platform API. No user data is "
"passed to the server or received in the response."
})");
} // namespace
ChallengeUrlFetcher::ChallengeUrlFetcher(
scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory)
: url_loader_factory_(std::move(url_loader_factory)) {}
ChallengeUrlFetcher::~ChallengeUrlFetcher() = default;
void ChallengeUrlFetcher::FetchUrl(GURL challenge_url,
base::OnceClosure callback) {
CHECK(!url_loader_);
CHECK(challenge_url.is_valid());
CHECK_EQ(state_, State::kFetchNotStarted);
FIDO_LOG(EVENT) << "Fetching request challenge from " << challenge_url;
auto resource_request = std::make_unique<network::ResourceRequest>();
resource_request->url = std::move(challenge_url);
resource_request->redirect_mode = network::mojom::RedirectMode::kError;
resource_request->credentials_mode = network::mojom::CredentialsMode::kOmit;
url_loader_ = network::SimpleURLLoader::Create(std::move(resource_request),
kTrafficAnnotation);
state_ = State::kFetchInProgress;
callback_ = std::move(callback);
url_loader_->DownloadToString(
url_loader_factory_.get(),
base::BindOnce(&ChallengeUrlFetcher::OnChallengeReceived,
weak_ptr_factory_.GetWeakPtr()),
kMaxChallengeSize);
}
void ChallengeUrlFetcher::OnChallengeReceived(
std::optional<std::string> response_body) {
CHECK_EQ(state_, State::kFetchInProgress);
state_ = State::kError;
auto* response_info = url_loader_->ResponseInfo();
int response_code = response_info && response_info->headers
? response_info->headers->response_code()
: url_loader_->NetError();
std::string content_type;
if (response_info && response_info->headers) {
response_info->headers->GetMimeType(&content_type);
}
url_loader_.reset();
if (response_code != net::HTTP_OK) {
FIDO_LOG(ERROR) << "Challenge fetch returned HTTP error " << response_code;
} else if (!response_body.has_value()) {
FIDO_LOG(ERROR) << "Challenge fetch returned no data";
} else if (content_type != kChallengeContentType) {
FIDO_LOG(ERROR)
<< "Challenge fetch encountered wrong content-type in response";
} else if (response_body->size() < kMinChallengeSize) {
FIDO_LOG(ERROR) << "Challenge obtained from fetch is too small";
} else {
challenge_ =
std::vector<uint8_t>(response_body->begin(), response_body->end());
state_ = State::kChallengeReceived;
}
std::move(callback_).Run();
}
base::expected<std::vector<uint8_t>,
ChallengeUrlFetcher::ChallengeNotAvailableReason>
ChallengeUrlFetcher::GetChallenge() {
switch (state_) {
case State::kFetchNotStarted:
return base::unexpected(ChallengeNotAvailableReason::kNotRequested);
case State::kFetchInProgress:
return base::unexpected(
ChallengeNotAvailableReason::kWaitingForChallenge);
case State::kChallengeReceived:
return base::ok(challenge_);
case State::kError:
return base::unexpected(
ChallengeNotAvailableReason::kErrorFetchingChallenge);
}
}
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