Added support for SSL/TLS

[moserware]

By design, Redis doesn't natively support encryption via SSL/TLS. However, it can be added with an SSL proxy.

For this reason, some popular Redis libraries support SSL connections.

This change adds support for SSL/TLS by leveraging asyncio's existing SSL support in asyncio.BaseEventLoop.create_connection and using its semantics.

I didn't exhaustively research or test this change, so this pull request is simply my first pass at how such a change might look. I welcome critical feedback on it.

Thanks for this library!

[coveralls]

Coverage decreased (-0.05%) to 92.389% when pulling 8dbbf99 on moserware:master into 9c8200a on aio-libs:master.

[asvetlov]

Please fix pep8 errors and add tests

[popravich]

Thanks for PR,
this looks good except few flake8 complaints.
I will take a closer look in a day or two.

[coveralls]

Coverage increased (+0.004%) to 92.447% when pulling 21241f3 on moserware:master into 9c8200a on aio-libs:master.

[moserware]

@asvetlov @popravich Thanks for the feedback! I fixed the PEP8 whitespace issues.

Regarding testing, I've only been using the ssl=True scenario (which uses defaults and works with a trusted certificate authority issued certificate)

It looks like when @oranagra of RedisLabs added SSL support to redis-py, he just noted that it worked with an SSL server.

One option is to create a self-signed certificate and then use stunnel locally. Perhaps with this setup, one could manually create the ssl.SSLContext and trust the generated certificate.

Any guidance on where I should go from here? I didn't know if you'd want to add something like stunnel to your testing environment.

Thanks again for your consideration of this PR!

P.S. Redislabs blog post when SSL was added to some popular clients.

[popravich]

The ssl parameter here must be keyword-only argument.

[moserware]

Thank you for cleaning this up and merging it! I look forward to using it via pip

[popravich]

I will do release this week.

[moserware]

👍 That'd be great. Thanks again!