QR code аuthorization

[IvanNazaruk]

Checklist

• The error is in the library's code, and not in my own.
• I have searched for this issue before posting it and there isn't a duplicate.
• I ran pip install -U https://github.com/LonamiWebs/Telethon/archive/master.zip and triggered the bug in the latest version.

Code that causes the issue

from telethon import TelegramClient
import asyncio

api_id = ""
api_hash = ""


def display_url_as_qr(url):
    print(url)
    pass  # do whatever to show url as a qr to the user


async def qr_login():
    client = TelegramClient('test', api_id, api_hash)
    await client.connect()

    qr_login = await client.qr_login()
    display_url_as_qr(qr_login.url)

    # Important! You need to wait for the login to complete!
    await qr_login.wait()
    print(await client.get_me())


loop = asyncio.get_event_loop()
loop.run_until_complete(qr_login())

Problem
When you scan the generated qr code, the application on the phone crashes: (click to open gif)

phone.mp4

But not always: (click to open gif)

phone_2.mp4

What's the problem?
The problem is that "qrlogin.py" uses base64 -> base64.b64encode(), as I understand it should be base64url -> urlsafe_b64encode().
I found url64 library, it has this code:

from base64 import urlsafe_b64encode, urlsafe_b64decode

__all__ = ['encode', 'decode']


def pad(s):
    return s + '=' * (4 - len(s) & 3)


def encode(s):
    if isinstance(s, str):
        s = s.encode()
    return urlsafe_b64encode(s).decode().rstrip("=")


def decode(s):
    return urlsafe_b64decode(pad(s)).decode()

and it does just fine:

import url64
return 'tg://login?token={}'.format(url64.encode(self._resp.token))

(I'm not suggesting that add this code to the library, it's just an example of how I fixed it)

What has changed?
Old:

tg://login?token=AQK/M89gA0PawCUIZe1cs5Y657FATBKcKfJ/C5NaQETbFQ==
tg://login?token=AQLcM89genyIgiSpZB6wmXJ2X3EKOma4x9MuAME/8ygXKA==
tg://login?token=AQL4M89gHX+0YcgqisVOiGSYEKlyz++1DbtOk9OfvDTxbg==

New:

tg://login?token=AQK_M89gA0PawCUIZe1cs5Y657FATBKcKfJ_C5NaQETbFQ
tg://login?token=AQLcM89genyIgiSpZB6wmXJ2X3EKOma4x9MuAME_8ygXKA
tg://login?token=AQL4M89gHX-0YcgqisVOiGSYEKlyz--1DbtOk9OfvDTxbg

[Lonami]

Thank you for the detailed report. Would you like to send a pull request? As I understand it, the changes needed are using base64.urlsafe_b64encode and adding .rstrip('=').