Stage 3 Tutorial - Login attempt fails : _Rendezvous of RPC that terminated with (StatusCode.UNAVAILABLE, Endpoint read failed

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Using ubuntu16.04. virtual_env version = 15.1.0. The setup instructions all seemed to install fine with no warnings. When i try to login to the webpage it fails. I signed the message as described, then pasted it to the box. then i get the Rendezvous error.

```
Environment:

Request Method: POST
Request URL: http://127.0.0.1:8000/verify/

Django Version: 1.11.1
Python Version: 2.7.12
Installed Applications:
['django.contrib.admin',
'django.contrib.auth',
'django.contrib.contenttypes',
'django.contrib.sessions',
'django.contrib.messages',
'whitenoise.runserver_nostatic',
'django.contrib.staticfiles',
'coindesk']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
'whitenoise.middleware.WhiteNoiseMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.middleware.common.CommonMiddleware',
'django.middleware.csrf.CsrfViewMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.contrib.messages.middleware.MessageMiddleware',
'django.middleware.clickjacking.XFrameOptionsMiddleware']

Traceback:

File "/home/febe/ln_workspace/deskenv/local/lib/python2.7/site-packages/django/core/handlers/exception.py" in inner
41. response = get_response(request)

File "/home/febe/ln_workspace/deskenv/local/lib/python2.7/site-packages/django/core/handlers/base.py" in _get_response
187. response = self.process_exception_by_middleware(e, request)

File "/home/febe/ln_workspace/deskenv/local/lib/python2.7/site-packages/django/core/handlers/base.py" in _get_response
185. response = wrapped_callback(request, *callback_args, **callback_kwargs)

File "/home/febe/ln_workspace/lightning-coindesk/coindesk/views.py" in verify
45. user = authenticate(request=request, **kwargs)

File "/home/febe/ln_workspace/deskenv/local/lib/python2.7/site-packages/django/contrib/auth/__init__.py" in authenticate
100. user = backend.authenticate(*args, **credentials)

File "/home/febe/ln_workspace/lightning-coindesk/coindesk/auth_backends.py" in authenticate
15. verifymessage_resp = stub.VerifyMessage(ln.VerifyMessageRequest(msg=csrf_token, signature=signature))

File "/home/febe/ln_workspace/deskenv/local/lib/python2.7/site-packages/grpc/_channel.py" in __call__
507. return _end_unary_response_blocking(state, call, False, deadline)

File "/home/febe/ln_workspace/deskenv/local/lib/python2.7/site-packages/grpc/_channel.py" in _end_unary_response_blocking
455. raise _Rendezvous(state, None, None, deadline)

Exception Type: _Rendezvous at /verify/
Exception Value: <_Rendezvous of RPC that terminated with (StatusCode.UNAVAILABLE, Endpoint read failed)>
```

Start by reproducing the failed POST to /verify/ and trace the flow through coindesk/views.py's verify entry point and coindesk/auth_backends.py's authenticate method, where VerifyMessage is called. Check the reported Django, Python, gRPC, and Ubuntu versions; done means the Stage 3 login completes successfully or the blocking cause is documented.

Written by the indexing model from the issue text.