I need my telegram bot to ask for the password, before letting a user to use the commands

I'm developing a telegram bot using the python library (telegram.ext) and I need that my bot accepts only the employees of my company. I do not want to use an authorization based on username, first/last name or chat_id, because in that way I have to add in the authorized list every new user, but I want to use some kind of password/keyword someone need to enter, before being able to use any command in the bot. The conversation flow would be like:

@Companybot:Welcome to the company bot, please enter your password!
@Employee: 12345test!
@CompanyBot: Password accepted! Please select a command from the command list!

I'm running the bot from my pc right now, not using any hosting service.

I tried to search in the internet for a solution but it seems that I'm asking the wrong questions, because I didn't find anything that could help me.

Thanks everybody for your help!

EDIT:

what i've tried is reported on https://github.com/python-telegram-bot/python-telegram-bot/wiki/Code-snippets#restrict-access-to-a-handler-decorator. This is the code I wrote:

def start(update, context):
    chat_id = update.message.chat_id
    first_name =update.message.chat.first_name
    last_name = update.message.chat.last_name
    username = update.message.chat.username
    print("chat_id : {} and firstname : {} lastname : {}  username {}". format(chat_id, first_name, last_name , username))
    context.bot.send_message(chat_id, 'Ciao ' + first_name + 'text')

 LIST_OF_ADMINS = [592769136]

def restricted(func):
    @wraps(func)
    def wrapped(update, context):
        user_id = update.effective_user.id
        if user_id not in LIST_OF_ADMINS:
            print("Unauthorized access denied for {}.".format(user_id))
        return
    return func(update, context)
return wrapped


def main():
    #updater (aggioramento):
    updater = Updater(token=token, use_context=True)

    #dispatcher (distribuzione aggiornamento):
    dispatcher = updater.dispatcher

    #lista di comandi da distribuire, ripresi dalle funzioni descritte all'inizio:

    @restricted
    start_handler = CommandHandler('start', start) # il comando è il primo termine, la funzione il secondo
    dispatcher.add_handler(start_handler)


    #comando per accendere il bot:
    updater.start_polling()
    updater.idle()


if __name__ == '__main__':
    main()

When I run the script, I get this error:

File "bot.py", line 88
    start_handler = CommandHandler('start', start) # il comando è il primo termine, la funzione il secondo
            ^
SyntaxError: invalid syntax

Because, it doesn't recognize the wrapper.

This is the only method I tried, I didn't find any other option.