Error 500 when switching from EncryptedCookieStorage to NaClCookieStorage

[tardyp]

  File "[..]/site-packages/aiohttp/web_protocol.py", line 390, in start
    resp = await self._request_handler(request)
  File "[..]/site-packages/aiohttp/web_app.py", line 366, in _handle
    resp = await handler(request)
  File "[..]/site-packages/aiohttp/web_middlewares.py", line 106, in impl
    return await handler(request)
  File "[..]/site-packages/aiohttp_session/__init__.py", line 149, in factory
    response = await handler(request)
  File "/Users/az02096/dev/nestor/elasticsearch_authorizations/elasticsearch_authorizations/app.py", line 122, in index_handler
    session = await get_session(request)
  File "[..]/site-packages/aiohttp_session/__init__.py", line 113, in get_session
    session = await storage.load_session(request)
  File "[..]/site-packages/aiohttp_session/nacl_storage.py", line 32, in load_session
    encoder=Base64Encoder).decode('utf-8')
  File "[..]/site-packages/nacl/secret.py", line 112, in decrypt
    ciphertext = encoder.decode(ciphertext)
  File "[..]/site-packages/nacl/encoding.py", line 73, in decode
    return base64.b64decode(data)
  File "[..]/base64.py", line 87, in b64decode
    return binascii.a2b_base64(s)
binascii.Error: Incorrect padding
INFO:aiohttp.access:::1 [10/Sep/2018:14:27:23 +0000] "GET / HTTP/1.1" 500 330 "http://localhost:8000/" 

Same issue when changing the secret.

probably we need to port this patch to NaClCookieStorage:
0741f5a

Not sure what is the benefit of NaClCookieStorage over EncryptedCookieStorage.

[asvetlov]

To process non-decodable data as a new session?

Makes sense to me.
Would you make a pull request?
BTW raising a warning if the data cannot be processed would be fine

[tardyp]

@asvetlov PR sent. I sniped in a doc fix as well