added option to request, require and verify client certificates

[SierraGolf]

currently the framework does not support the 3rd parameter checkClientCertificate of the grpc.ServerCredentials.createSsl function. this pull request adds support for it.

[coveralls]

Coverage remained the same at 100.0% when pulling 7d27b07 on SierraGolf:master into a1ea74b on devsu:master.

[SierraGolf]

@c3s4r can you have a look at this?

[c3s4r]

Hi @SierraGolf, thanks for the PR. I haven't had a chance to review it (on vacations now), but I'll take a look early next week.

[c3s4r]

Hi @SierraGolf, the PR looks good, the only missing piece is a test with checkClientCert = true. Please add it if possible, and I will merge the change. Otherwise, I will do it but not now, since I'll be busy on other urgent projects. Thanks!

[SierraGolf]

I think a test similar to this one would make sense:
https://github.com/SierraGolf/condor-framework/blob/7d27b07f5294984490b0a134c212b1b00f06fced/lib/server.spec.js#L230

However, the test currently cannot assert on the properties of the credentials object, so we would need to spy on this somehow. Not sure what is the best approach to do that.

[c3s4r]

Ok, thanks. I'll take a look hopefully during next week.

[SierraGolf]

any chance this will get merged and released?