All requests to Plivo API are authenticated with BasicAuth using your AUTH ID and AUTH TOKEN. You can see your Plivo AUTH ID and AUTH TOKEN at the top of the Overview page of the Plivo console. Example Request 
import plivo

proxies = {
    'http': 'https://username:password@proxyurl:proxyport',
    'https': 'https://username:password@proxyurl:proxyport'
    }
client = plivo.RestClient('<auth_id>', '<auth_token>', proxies=proxies,timeout=5)