A polyfill for PHP bug https://bugs.php.net/bug.php?id=62372

crypt_sha.php

<?php

define('CRYPT_SALT_LEN_MAX', 16);
define('CRYPT_ROUNDS_DEFAULT', 5000);

/**
 * A PHP shim for crypt sha256 and sha512
 * to workaround bug 62372
 * @see https://bugs.php.net/bug.php?id=62372
 */
function crypt_sha($password, $salt) {
    if (!in_array(substr($salt, 0, 3), array('$5$', '$6$'))) return false;
    $algo = $salt[1] === '5' ? 'sha256' : 'sha512';
    $padLen = $salt[1] === '5' ? 32 : 64;
    $salt = substr($salt, 3);
    $rounds = CRYPT_ROUNDS_DEFAULT;
    $roundsCustom = false;
    if (preg_match('(^rounds=(\d+)\$)i', $salt, $match)) {
        $rounds = (int) $match[1];
        $salt = substr($salt, strlen($match[0]));
        $roundsCustom = true;
    }
    $saltLen = min(strcspn($salt, '$'), CRYPT_SALT_LEN_MAX);
    $salt = substr($salt, 0, $saltLen);
    $ctx = hash_init($algo);
    hash_update($ctx, $password);
    hash_update($ctx, $salt);
    $alt = hash($algo, $password . $salt . $password, true);
    for ($i = strlen($password); $i > $padLen; $i -= $padLen) {
        hash_update($ctx, substr($alt, 0, $padLen));
    }
    hash_update($ctx, substr($alt, 0, $i));
    for ($i = strlen($password); $i > 0; $i >>= 1) {
        if (($i & 1) != 0) {
            hash_update($ctx, substr($alt, 0, $padLen));
        } else {
            hash_update($ctx, $password);
        }
    }
    $alt = hash_final($ctx, true);
    $temp = hash($algo, str_repeat($password, strlen($password)), true);
    $p = substr(str_repeat($temp, ceil(strlen($password) % $padLen)), 0, strlen($password));
    $temp = hash($algo, str_repeat($salt, ord($alt[0])+16), true);
    $s = substr(str_repeat($temp, ceil(strlen($salt) % $padLen)), 0, strlen($salt));

    for ($i = 0; $i < $rounds; $i++) {
        $altCtx = hash_init($algo);
        if (($i & 1) != 0) {
            hash_update($altCtx, $p);
        } else {
            hash_update($altCtx, $alt);
        }
        if (($i % 3) != 0) {
            hash_update($altCtx, $s);
        }
        if (($i % 7) != 0) {
            hash_update($altCtx, $p);
        }
        if (($i & 1) != 0) {
            hash_update($altCtx, $alt);
        } else {
            hash_update($altCtx, $p);
        }
        $alt = hash_final($altCtx, true);
    }
    $result = $algo === 'sha256' ? '$5$' : '$6$';
    if ($roundsCustom) {
        $result .= 'rounds=' . $rounds . '$';
    }
    $result .= $salt . '$';
    if ($algo == 'sha256') {
        $result .= encode_sha256_crypt($alt);
    } else {
        $result .= encode_sha512_crypt($alt);
    }
    return $result;
}


function encode_sha256_crypt($alt) {
    $result = b64_from_b24($alt[0], $alt[10], $alt[20], 4);
    $result .= b64_from_b24($alt[21], $alt[1], $alt[11], 4);
    $result .= b64_from_b24($alt[12], $alt[22], $alt[2], 4);
    $result .= b64_from_b24($alt[3], $alt[13], $alt[23], 4);
    $result .= b64_from_b24($alt[24], $alt[4], $alt[14], 4);
    $result .= b64_from_b24($alt[15], $alt[25], $alt[5], 4);
    $result .= b64_from_b24($alt[6], $alt[16], $alt[26], 4);
    $result .= b64_from_b24($alt[27], $alt[7], $alt[17], 4);
    $result .= b64_from_b24($alt[18], $alt[28], $alt[8], 4);
    $result .= b64_from_b24($alt[9], $alt[19], $alt[29], 4);
    $result .= b64_from_b24(chr(0), $alt[31], $alt[30], 3);
    return $result;
}

function encode_sha512_crypt($alt) {
    $result = b64_from_b24($alt[0], $alt[21], $alt[42], 4);
    $result .= b64_from_b24($alt[22], $alt[43], $alt[1], 4);
    $result .= b64_from_b24($alt[44], $alt[2], $alt[23], 4);
    $result .= b64_from_b24($alt[3], $alt[24], $alt[45], 4);
    $result .= b64_from_b24($alt[25], $alt[46], $alt[4], 4);
    $result .= b64_from_b24($alt[47], $alt[5], $alt[26], 4);
    $result .= b64_from_b24($alt[6], $alt[27], $alt[48], 4);
    $result .= b64_from_b24($alt[28], $alt[49], $alt[7], 4);
    $result .= b64_from_b24($alt[50], $alt[8], $alt[29], 4);
    $result .= b64_from_b24($alt[9], $alt[30], $alt[51], 4);
    $result .= b64_from_b24($alt[31], $alt[52], $alt[10], 4);
    $result .= b64_from_b24($alt[53], $alt[11], $alt[32], 4);
    $result .= b64_from_b24($alt[12], $alt[33], $alt[54], 4);
    $result .= b64_from_b24($alt[34], $alt[55], $alt[13], 4);
    $result .= b64_from_b24($alt[56], $alt[14], $alt[35], 4);
    $result .= b64_from_b24($alt[15], $alt[36], $alt[57], 4);
    $result .= b64_from_b24($alt[37], $alt[58], $alt[16], 4);
    $result .= b64_from_b24($alt[59], $alt[17], $alt[38], 4);
    $result .= b64_from_b24($alt[18], $alt[39], $alt[60], 4);
    $result .= b64_from_b24($alt[40], $alt[61], $alt[19], 4);
    $result .= b64_from_b24($alt[62], $alt[20], $alt[41], 4);
    $result .= b64_from_b24(chr(0), chr(0), $alt[63], 2);

    return $result;
}

function b64_from_b24($a, $b, $c, $n) {
    static $b64t = "./0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
    $w = (ord($a) << 16) | (ord($b) << 8) | ord($c);
    $ret = '';
    while ($n-- > 0) {
        $ret .= $b64t[$w & 0x3f];
        $w >>= 6;
    }
    return $ret;
}