system: You are an expert security code reviewer. You will be shown a source code file along with a multiple-choice question listing several function or class names from that file. Your task is to identify which one contains the specified CWE vulnerability.

OUTPUT FORMAT: Respond with the single letter of the correct option, wrapped in \boxed{...}. Example: `\boxed{B}`. Output the boxed letter ONLY -- no explanation, no other text.

user: ```python
"""Traefik installation and setup"""
import hashlib
import os
from glob import glob

from jinja2 import Template
from passlib.apache import HtpasswdFile
import backoff
import requests
import toml

from .config import CONFIG_DIR
from tljh.configurer import load_config, _merge_dictionaries

# FIXME: support more than one platform here
plat = "linux-amd64"
traefik_version = "1.7.18"

# record sha256 hashes for supported platforms here
checksums = {
    "linux-amd64": "3c2d153d80890b6fc8875af9f8ced32c4d684e1eb5a46d9815337cb343dfd92e"
}

def checksum_file(path):
    """Compute the sha256 checksum of a path"""
    hasher = hashlib.sha256()
    with open(path, "rb") as f:
        for chunk in iter(lambda: f.read(4096), b""):
            hasher.update(chunk)
    return hasher.hexdigest()

def fatal_error(e):
    # Retry only when connection is reset or we think we didn't download entire file
    return str(e) != "ContentTooShort" and not isinstance(e, ConnectionResetError)

@backoff.on_exception(
    backoff.expo,
    Exception,
    max_tries=2,
    giveup=fatal_error
)
def ensure_traefik_binary(prefix):
    """Download and install the traefik binary"""
    traefik_bin = os.path.join(prefix, "bin", "traefik")
    if os.path.exists(traefik_bin):
        checksum = checksum_file(traefik_bin)
        if checksum == checksums[plat]:
            # already have the right binary
            # ensure permissions and we're done
            os.chmod(traefik_bin, 0o755)
            return
        else:
            print(f"checksum mismatch on {traefik_bin}")
            os.remove(traefik_bin)

    traefik_url = (
        "https://github.com/containous/traefik/releases"
        f"/download/v{traefik_version}/traefik_{plat}"
    )
    print(f"Downloading traefik {traefik_version}...")
    # download the file
    response = requests.get(traefik_url)
    if response.status_code == 206:
        raise Exception("ContentTooShort")
    with open(traefik_bin, 'wb') as f:
        f.write(response.content)
    os.chmod(traefik_bin, 0o755)

    # verify that we got what we expected
    checksum = checksum_file(traefik_bin)
    if checksum != checksums[plat]:
        raise IOError(f"Checksum failed {traefik_bin}: {checksum} != {checksums[plat]}")


def compute_basic_auth(username, password):
    """Generate hashed HTTP basic auth from traefik_api username+password"""
    ht = HtpasswdFile()
    # generate htpassword
    ht.set_password(username, password)
    hashed_password = str(ht.to_string()).split(":")[1][:-3]
    return username + ":" + hashed_password


def load_extra_config(extra_config_dir):
    extra_configs = sorted(glob(os.path.join(extra_config_dir, '*.toml')))
    # Load the toml list of files into dicts and merge them
    config = toml.load(extra_configs)
    return config


def ensure_traefik_config(state_dir):
    """Render the traefik.toml config file"""
    traefik_std_config_file = os.path.join(state_dir, "traefik.toml")
    traefik_extra_config_dir = os.path.join(CONFIG_DIR, "traefik_config.d")
    traefik_dynamic_config_dir = os.path.join(state_dir, "rules")

    config = load_config()
    config['traefik_api']['basic_auth'] = compute_basic_auth(
        config['traefik_api']['username'],
        config['traefik_api']['password'],
    )

    with open(os.path.join(os.path.dirname(__file__), "traefik.toml.tpl")) as f:
        template = Template(f.read())
    std_config = template.render(config)
    https = config["https"]
    letsencrypt = https["letsencrypt"]
    tls = https["tls"]
    # validate https config
    if https["enabled"]:
        if not tls["cert"] and not letsencrypt["email"]:
            raise ValueError(
                "To enable https, you must set tls.cert+key or letsencrypt.email+domains"
            )
        if (letsencrypt["email"] and not letsencrypt["domains"]) or (
            letsencrypt["domains"] and not letsencrypt["email"]
        ):
            raise ValueError("Both email and domains must be set for letsencrypt")

    # Ensure traefik extra static config dir exists and is private
    os.makedirs(traefik_extra_config_dir, mode=0o700, exist_ok=True)

    # Ensure traefik dynamic config dir exists and is private
    os.makedirs(traefik_dynamic_config_dir, mode=0o700, exist_ok=True)

    try:
        # Load standard config file merge it with the extra config files into a dict
        extra_config = load_extra_config(traefik_extra_config_dir)
        new_toml = _merge_dictionaries(toml.loads(std_config), extra_config)
    except FileNotFoundError:
        new_toml = toml.loads(std_config)

    # Dump the dict into a toml-formatted string and write it to file
    with open(traefik_std_config_file, "w") as f:
        os.fchmod(f.fileno(), 0o600)
        toml.dump(new_toml, f)

    with open(os.path.join(traefik_dynamic_config_dir, "rules.toml"), "w") as f:
        os.fchmod(f.fileno(), 0o600)

    # ensure acme.json exists and is private
    with open(os.path.join(state_dir, "acme.json"), "a") as f:
        os.fchmod(f.fileno(), 0o600)


```

Which of the following functions or classes contains a `CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')` vulnerability?

  A) checksum_file
  B) compute_basic_auth
  C) ensure_traefik_binary
  D) ensure_traefik_config
Answer: D