Differential D19946 Diff 47638 src/applications/auth/engine/PhabricatorAuthCSRFEngine.php

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src/applications/auth/engine/PhabricatorAuthCSRFEngine.php

This file was added.

				<?php

				final class PhabricatorAuthCSRFEngine extends Phobject {

				private $salt;
				private $secret;

				public function setSalt($salt) {
				$this->salt = $salt;
				return $this;
				}

				public function getSalt() {
				return $this->salt;
				}

				public function setSecret(PhutilOpaqueEnvelope $secret) {
				$this->secret = $secret;
				return $this;
				}

				public function getSecret() {
				return $this->secret;
				}

				public function newSalt() {
				$salt_length = $this->getSaltLength();
				return Filesystem::readRandomCharacters($salt_length);
				}

				public function newToken() {
				$salt = $this->getSalt();

				if (!$salt) {
				throw new PhutilInvalidStateException('setSalt');
				}

				$token = $this->newRawToken($salt);
				$prefix = $this->getBREACHPrefix();

				return sprintf('%s%s%s', $prefix, $salt, $token);
				}

				public function isValidToken($token) {
				$salt_length = $this->getSaltLength();

				// We expect a BREACH-mitigating token. See T3684.
				$breach_prefix = $this->getBREACHPrefix();
				$breach_prelen = strlen($breach_prefix);
				if (strncmp($token, $breach_prefix, $breach_prelen) !== 0) {
				return false;
				}

				$salt = substr($token, $breach_prelen, $salt_length);
				$token = substr($token, $breach_prelen + $salt_length);

				foreach ($this->getWindowOffsets() as $offset) {
				$expect_token = $this->newRawToken($salt, $offset);
				if (phutil_hashes_are_identical($expect_token, $token)) {
				return true;
				}
				}

				return false;
				}

				private function newRawToken($salt, $offset = 0) {
				$now = PhabricatorTime::getNow();
				$cycle_frequency = $this->getCycleFrequency();

				$time_block = (int)floor($now / $cycle_frequency);
				$time_block = $time_block + $offset;

				$secret = $this->getSecret();
				if (!$secret) {
				throw new PhutilInvalidStateException('setSecret');
				}
				$secret = $secret->openEnvelope();

				$hash = PhabricatorHash::digestWithNamedKey(
				$secret.$time_block.$salt,
				'csrf');

				return substr($hash, 0, $this->getTokenLength());
				}

				private function getBREACHPrefix() {
				return 'B@';
				}

				private function getSaltLength() {
				return 8;
				}

				private function getTokenLength() {
				return 16;
				}

				private function getCycleFrequency() {
				return phutil_units('1 hour in seconds');
				}

				private function getWindowOffsets() {
				// We accept some tokens from the recent past and near future. Users may
				// have older tokens if they close their laptop and open it up again
				// later. Users may have newer tokens if there are multiple web hosts with
				// a bit of clock skew.

				// Javascript on the client tries to keep CSRF tokens up to date, but
				// it may fail, and it doesn't run if the user closes their laptop.

				// The window during which our tokens remain valid is generally more
				// conservative than other platforms. For example, Rails uses "session
				// duration" and Django uses "forever".

				return range(-6, 1);
				}

				}