Adhere to PSR-7/PSR-17/PSR-18

[flavioheleno]

The code right now uses some ad-hoc curl requests for both domain and certificate checks, this obviously is sub-optimal as it will be hard to write tests to it.

Another point is that some of the dependencies also ship their own HTTP Client implementation as part of their code, which means that we have code duplication here and there.

Ideally the best solution would be to adhere to HTTP related PSRs (PSR-7/PSR-17/PSR-18) and try to contribute back to the dependencies as well.