import re
url = 'https://x...content-available-to-author-only...k.ru/?code=884gdczv72ka3kkco6sxoen2ugp380y1&state=&domain=xxx.omsk.ru'
m = re.search(r'[&?]code=([^&]+)', url)
if m:
print(m.group(1))
aW1wb3J0IHJlCnVybCA9ICdodHRwczovL3guLi5jb250ZW50LWF2YWlsYWJsZS10by1hdXRob3Itb25seS4uLmsucnUvP2NvZGU9ODg0Z2RjenY3MmthM2trY282c3hvZW4ydWdwMzgweTEmc3RhdGU9JmRvbWFpbj14eHgub21zay5ydScKbSA9IHJlLnNlYXJjaChyJ1smP11jb2RlPShbXiZdKyknLCB1cmwpCmlmIG06CglwcmludChtLmdyb3VwKDEpKQ==