Yggdrasil Authentication implementation for Minecraft, implements all known Yggdrasil methods and is a lot simpler than some of the other implementations floating around

yggdrasil.py

import urllib.request as request
from urllib.error import HTTPError
import json

class YggAuth:
	def __init__(self, 
		client_token=None, 
		access_token=None, 
		username=None, 
		password=None
	):
		self.username = username
		self.password = password
		self.client_token = client_token

		self.access_token = None #validate needs access_token to exist
		self.access_token = (
			None if self.validate(access_token) else access_token
		)

	def _gen_req(self, endpoint, payload):
		url = 'https://authserver.mojang.com' + endpoint
		data = json.dumps(payload).encode('utf-8')
		headers = {'Content-Type': 'application/json'}
		return request.Request(url, data, headers, method='POST')

	def _gen_rep(self, req):
		try:
			rep = request.urlopen(req)
		except HTTPError as reperr:
			rep = reperr
		data = rep.read().decode('utf-8')
		return json.loads(data) if data else None

	def _ygg_req(self, endpoint, payload):
		return self._gen_rep(self._gen_req(endpoint, payload))

	#Generate an access token using a username and password
	#(Any existing client token is invalidated if not provided)
	#Returns response dict on success, otherwise error dict
	def authenticate(self, username=None, password=None, client_token=None):
		endpoint = '/authenticate'
		payload = {
			'agent': {
				'name': 'Minecraft',
				'version': 1,
			},
		}
		if username:
			self.username = username
		payload['username'] = self.username
		if password:
			self.password = password
		payload['password'] = self.password
		payload['clientToken'] = client_token if client_token else self.client_token
		rep = self._ygg_req(endpoint, payload)
		if 'error' not in rep:
			self.access_token = rep['accessToken']
			self.client_token = rep['clientToken']
		return rep

	#Generate an access token with a client/access token pair
	#(The used access token is invalidated)
	#Returns response dict on success, otherwise error dict
	def refresh(self, client_token=None, access_token=None):
		endpoint = '/refresh'
		payload = {}
		payload['accessToken'] = access_token if access_token else self.access_token
		payload['clientToken'] = client_token if client_token else self.client_token
		rep = self._ygg_req(endpoint, payload)
		if 'error' not in rep:
			self.access_token = rep['accessToken']
			self.client_token = rep['clientToken']
		return rep

	#Invalidate access tokens with a username and password
	#Returns None on success, otherwise error dict
	def signout(self, username=None, password=None):
		endpoint = '/signout'
		payload = {}
		payload['username'] = username if username else self.username
		payload['password'] = password if password else self.password
		return self._ygg_req(endpoint, payload)

	#Invalidate access tokens with a client/access token pair
	#Returns None on success, otherwise error dict
	def invalidate(self, client_token=None, access_token=None):
		endpoint = '/invalidate'
		payload = {}
		payload['accessToken'] = access_token if access_token else self.access_token
		payload['clientToken'] = client_token if client_token else self.client_token
		return self._ygg_req(endpoint, payload)

	#Check if an access token is valid
	#Returns None on success (ie valid access token), otherwise error dict
	def validate(self, access_token=None):
		endpoint = '/validate'
		payload = {}
		payload['accessToken'] = access_token if access_token else self.access_token
		return self._ygg_req(endpoint, payload)

But how can i optain a session id?

very cool