xajax=login&xajaxs=[PHPSESSID]&xajaxr=1535661804261&xajaxargs[]=aaa&xajaxargs[]=aaa&xajaxargs[]=S&xajaxargs[]=&xajaxargs[]=

USERNAME='xxxxxx'
PASSWORD='xxxxxx'
import requests
loginURL = 'https://www.bling.com.br/login?r="'
headers = {'User-Agente':'Mozilla/5.0',
               'Referer':'https://www.bling.com.br/login'}
login_data = dict(username=USERNAME,senha=PASSWORD)
c = requests.Session()
c.post(loginURL,data=login_data,headers=headers)
page = c.get('https://www.bling.com.br')
print(page.content)