#import libraries
import csv
import requests
from bs4 import BeautifulSoup

URL="http://thuvientulap.org/login.aspx"

username="user"
password="password"

s=requests.Session()
r=s.get(URL)

soup=BeautifulSoup(r.content,'html.parser')

VIEWSTATE=soup.find(id="__VIEWSTATE")['value']
EVENTVALIDATION=soup.find(id="__EVENTVALIDATION")['value']
VIEWSTATEGENERATOR=soup.find(id="__VIEWSTATEGENERATOR")['value']

login_data={"__VIEWSTATE":VIEWSTATE,
"txt_name_login":username,
"txt_password_ogin":password,
"__VIEWSTATE":VIEWSTATE,
"__EVENTVALIDATION":EVENTVALIDATION,
"__VIEWSTATEGENERATORT":VIEWSTATEGENERATOR,
}

r = s.post(URL, data=login_data)

admin_url =("http://thuvientulap.org/admin.aspx")
r = s.get(admin_url)

print (r.url)
print (r.text)

import requests
s=requests.Session()
url ="http://thuvientulap.org/login.aspx"
r=s.get(url)
dct=s.cookies.get_dict()#you will get a ASP.net cookie pass it in header
                         along with other headers


aid=dct["ASP.NETID"]*
head = {ASP.NETID=jid,.....}*
*check for the correct ASPid-name in request headers
r = s.post(url, data=login_data,headers=head)