Get an `access code` without running a webserver or interacting with a browser. Makes interacting with the Web API remotely more convenient.

tradestation_headless_auth.py

import requests
import json
from urllib.parse import unquote
from selenium import webdriver
from selenium.webdriver.firefox.options import Options

API_KEY = '*******' # Also called the `client_id`
SECRET_KEY = '*******'
REDIRECT_URI = 'http://localhost:8080' # Arbitrary for headless.
BASE_URL = 'https://sim-api.tradestation.com/v2'
USERNAME = "*******"
PASSWORD = "*******"

#
# Security questions and answers...
#
QUESTION_ONE = "*******"
QUESTION_TWO = "*******"
QUESTION_THREE = "*******"

ANSWER_ONE = "*******"
ANSWER_TWO = "*******"
ANSWER_THREE = "*******"

#
# Once we have the auth code, we can exchange it for the refresh token and access token.
#
def get_token_response(access_code):
    headers = {'Content-Type': 'application/x-www-form-urlencoded'}
    post_data = {
            'grant_type': 'authorization_code',
            'client_id': API_KEY,
            'client_secret': SECRET_KEY,
            'redirect_uri': REDIRECT_URI,
            'code': access_code
        }
    r = requests.post(f'{BASE_URL}/Security/Authorize', headers=headers, data=post_data)
    try:
        return r.json()
    except:
        return sys.exc_info()[0]


#
# Start Selenium...
#
options = Options()
options.headless = True

driver = webdriver.Firefox(options=options)

auth_url = f"{BASE_URL}/authorize?redirect_uri={REDIRECT_URI}&client_id={API_KEY}&response_type=code"

try:
    driver.get(auth_url)

    elem = driver.find_element_by_name("username")
    elem.clear()
    elem.send_keys(USERNAME)

    elem = driver.find_element_by_name("password")
    elem.clear()
    elem.send_keys(PASSWORD)

    driver.find_element_by_id("btnLogin").click()

    elem = driver.find_element_by_name("ucQuestionAndAnswer$txtAnswer")
    elem.clear()

    if QUESTION_ONE in driver.page_source:
        elem.send_keys(ANSWER_ONE)
    elif QUESTION_TWO in driver.page_source:
        elem.send_keys(ANSWER_TWO)
    elif QUESTION_THREE in driver.page_source:
        elem.send_keys(ANSWER_THREE)
    else:
        print("Uh oh...") # Should probabaly raise exception here.

    driver.find_element_by_id("ucQuestionAndAnswer_btnLogin").click()

#
#  Lol. If you know a better way to do this, please let me know.
#
except Exception as e:
    s = unquote(e.msg) # `e.msg` is in UTF-8, using `unquote` just makes it easier to read/find the start of the access_code from the error message.  Not necessary, however.
    a, b = s.find("code="), s.find("&c=UTF-8")
    access_code = (s[a+5:b]) # The `+5` here is just the length of the string you used to `find` the start of the access_code.

token_response = get_token_response(access_code)
refresh_token = token_response['refresh_token']
access_token = token_response['access_token']

print("--- Token Response ---")
print(token_response)
print("--- Access Code ---")
print(access_code)
print("--- Access Token ---")
print(access_token)
print("--- Refresh Token ---")
print(refresh_token)

driver.close()