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
# This code is based on https://github.com/delucks/gtd.py onboard function,
# especial thanks to: delucks
import yaml
import os
import webbrowser
import trello
import sys
import configuration
from requests_oauthlib import OAuth1Session
from requests_oauthlib.oauth1_session import TokenRequestDenied

import logging
logging.basicConfig(filename='Running.log',level=logging.INFO, format='%(asctime)s:%(levelname)s:%(message)s')

class DevNullRedirect:
    '''Temporarily eat stdout/stderr to allow no output.
    This is used to suppress browser messages in webbrowser.open'''

    def __enter__(self):
        self.old_stderr = os.dup(2)
        self.old_stdout = os.dup(1)
        os.close(2)
        os.close(1)
        os.open(os.devnull, os.O_RDWR)

    def __exit__(self, exc_type, exc_value, traceback):
        os.dup2(self.old_stderr, 2)
        os.dup2(self.old_stdout, 1)


def onboard(no_open, output_path='polical.yaml'):
    '''Obtain Trello API credentials and put them into your config file.
    This is invoked automatically the first time you attempt to do an operation which requires authentication.
    The configuration file is put in an appropriate place for your operating system. If you want to change it later,
    you can use `gtd config -e` to open it in $EDITOR.
    '''
    output_file = output_path  # Use platform detection
    user_api_key_url = 'https://trello.com/app-key'
    request_token_url = 'https://trello.com/1/OAuthGetRequestToken'
    authorize_url = 'https://trello.com/1/OAuthAuthorizeToken'
    access_token_url = 'https://trello.com/1/OAuthGetAccessToken'
    calendar_moodle_epn_url = 'https://educacionvirtual.epn.edu.ec/calendar/view.php?view=upcoming&course=1'
    # First, open the URL that allows the user to get an auth token. Tell them to copy both into the program
    logging.info("Mostrando print-board al usuario")
    print('Bienvenido a PoliCal! Recuerde que antes de iniciar el proceso de obtención de credenciales')
    print('ud debe tener una cuenta en Trello y en el Aula Virtual, y deben estar iniciadas las sesiones en el navegador predeterminado')
    print("\n\n")
    print("PASO 1: Acceso a Trello")
    print("En su navegador web se cargará el siguiente URL:")
    print('  ' + user_api_key_url)
    print('Cuando llegue a esa página, inicie sesión y copie la "Tecla" o "Key" que se muestra en un cuadro de texto.')
    print('Si es la primera vez que realiza este proceso debe aceptar los terminos y condiciones de Trello')
    input("Presione ENTER para ir al enlace")
    if not no_open:
        with DevNullRedirect():
            webbrowser.open_new_tab(user_api_key_url)
    api_key = input('Por favor, introduzca el valor de "Tecla" o "Key":')
    print('Ahora desplácese hasta la parte inferior de la página y copie el "Secreto" o "Secret" que se muestra en un cuadro de texto.')
    api_secret = input('Por favor, introduzca el valor de "Secret":')
    # Then, work on getting OAuth credentials for the user so they are permanently authorized to use this program
    print("\n\n")
    print("PASO 2: Permitir acceso de Polical a Trello")
    print('Ahora obtendremos las credenciales de OAuth necesarias para usar este programa...')
    # The following code is cannibalized from trello.util.create_oauth_token from the py-trello project.
    # Rewriting because it does not support opening the auth URLs using webbrowser.open and since we're using
    # click, a lot of the input methods used in that script are simplistic compared to what's available to us.
    # Thank you to the original authors!
    '''Step 1: Get a request token. This is a temporary token that is used for
    having the user authorize an access token and to sign the request to obtain
    said access token.'''
    session = OAuth1Session(client_key=api_key, client_secret=api_secret)
    try:
        response = session.fetch_request_token(request_token_url)
    except TokenRequestDenied:
        print('Invalid API key/secret provided: {0} / {1}'.format(api_key, api_secret))
        sys.exit(1)
    resource_owner_key, resource_owner_secret = response.get(
        'oauth_token'), response.get('oauth_token_secret')
    '''Step 2: Redirect to the provider. Since this is a CLI script we do not
    redirect. In a web application you would redirect the user to the URL
    below.'''
    user_confirmation_url = '{authorize_url}?oauth_token={oauth_token}&scope={scope}&expiration={expiration}&name={name}'.format(
        authorize_url=authorize_url,
        oauth_token=resource_owner_key,
        expiration='never',
        scope='read,write',
        name='PoliCal',
    )
    print('Visite la siguiente URL en su navegador web para autorizar a PoliCal acceso a su cuenta:')
    print('  ' + user_confirmation_url)
    print("Concedale los permisos a PoliCal para acceder a sus datos de Trello, estas credenciales se mantendran de manera local")
    input("Presione ENTER para ir al enlace")
    if not no_open:
        with DevNullRedirect():
            webbrowser.open_new_tab(user_confirmation_url)
    '''After the user has granted access to you, the consumer, the provider will
    redirect you to whatever URL you have told them to redirect to. You can
    usually define this in the oauth_callback argument as well.'''
    confirmation = input(
        '¿Has autorizado a PoliCal? Escriba n para no y S para si:')
    while confirmation == "n":
        confirmation = input(
            '¿Has autorizado a PoliCal? Escriba n para no y S para si:')

    oauth_verifier = input('¿Cuál es el código de verificación?:').strip()
    '''Step 3: Once the consumer has redirected the user back to the oauth_callback
    URL you can request the access token the user has approved. You use the
    request token to sign this request. After this is done you throw away the
    request token and use the access token returned. You should store this
    access token somewhere safe, like a database, for future use.'''
    session = OAuth1Session(
        client_key=api_key,
        client_secret=api_secret,
        resource_owner_key=resource_owner_key,
        resource_owner_secret=resource_owner_secret,
        verifier=oauth_verifier,
    )
    access_token = session.fetch_access_token(access_token_url)

    '''Step 4: Ahora se debe buscar el calendario en formato ICS generado por el
    Aula Virtual'''
    print("\n\n")
    print("PASO 3: Obtención del calendario del Aula Virtual")
    print("A continuación se abrirá un link hacia el Aula Virtual EPN, en proximos eventos para: elija Todos los cursos")
    print("y a continuación desplácese a la parte más inferior de la página y de clic en el botón Exportar Calendario")
    print("Luego, en la opción Exportar seleccione todos los eventos y después en \"para\" seleccione los 60 días recientes y próximos")
    print("Finalmente de clic en el boton Obtener URL del calendario")
    print('Visite la siguiente URL en su navegador web para obtener el calendario del aula virtual EPN:')
    print('  ' + calendar_moodle_epn_url)
    input("Presione ENTER para ir al enlace e iniciar el proceso, no olvide verificar si su sesión del Aula Virtual se encuentra activa")
    if not no_open:
        with DevNullRedirect():
            webbrowser.open_new_tab(calendar_moodle_epn_url)
    calendar_url = calendar_moodle_epn_url
    while not(configuration.check_for_url(calendar_url)):
        calendar_url = input('Por favor, introduzca el url generado por el Aula Virtual, si este es erróneo se volverá a solicitar:')
    final_output_data = {
        'oauth_token': access_token['oauth_token'],
        'oauth_token_secret': access_token['oauth_token_secret'],
        'api_key': api_key,
        'api_secret': api_secret,
        'calendar_url': calendar_url,
    }
    # Ensure we have a folder to put this in, if it's in a nested config location
    """
    output_folder = os.path.dirname(output_file)
    if not os.path.isdir(output_folder):
        os.makedirs(output_folder)
        print('Created folder {0} to hold your configuration'.format(output_folder))
    # Try to be safe about not destroying existing credentials
    """
    board_id, owner_id = get_working_board_id(
        api_key, api_secret, access_token['oauth_token'], access_token['oauth_token_secret'])
    final_output_data['board_id'] = board_id
    final_output_data['owner_id'] = owner_id
    if os.path.exists(output_file):
        # if input('{0} exists already, would you like to back it up?'.format(output_file)):
        #    shutil.move(output_file, output_file + '.backup')
        overwrite = input('Overwrite the existing file? s/N:')
        if overwrite == 'N':
            return
    with open(output_file, 'w') as f:
        f.write(yaml.safe_dump(final_output_data, default_flow_style=False))
    #print('Las credenciales se guardaron en "{0}"- ahora puedes utilizar PoliCal'.format(output_file))
    #print('Use the "config" command to view or edit your configuration file')


def get_working_board_id(api_key, api_secret, oauth_token, oauth_token_secret):
    client = trello.TrelloClient(
        api_key=api_key,
        api_secret=api_secret,
        token=oauth_token,
        token_secret=oauth_token_secret,
    )
    board_id = ''
    all_boards = client.list_boards()
    for board in all_boards:
        if board.name == "TareasPoli":
            board_id = board.id
    if board_id == '':
        logging.error(("No se encontró el board \"TareasPoli\", será creado ahora"))
        print("No se encontró el board \"TareasPoli\", será creado ahora")
        client.add_board("TareasPoli")
        all_boards = client.list_boards()
        for board in all_boards:
            if board.name == "TareasPoli":
                board_id = board.id
    return board_id, board.all_members()[-1].id

# onboard(True)

```

Which of the following functions or classes contains a `CWE-312: Cleartext Storage of Sensitive Information` vulnerability?

  A) onboard
  B) DevNullRedirect
  C) __enter__
  D) get_working_board_id
Answer: A