TLS Client Authentication

[h0tw1r3]

Feature request. Alternative to htpasswd auth.

[wojas]

PR #140 also implements TLS client auth with automatic certificate reload through https://github.com/PowerDNS/go-tlsconfig . I can rebase the PR in the next few weeks.

[smiller255]

There are currently three PRs what implement this feature:
#140
#191
#193

@MichaelEischer I would like to work on this issue to get TLS client authentication implemented soon. Can you say what is required for this to happen and which one of these PRs look most promising to you to be merged? If you can name specific changes you would like to see, I would like to work on this.

It looks to me like #193 is the only one using the official go crypto lib, therefore I would argue for this to be used.