Go's C FFI support does exist and there are OpenSSL bindings. But CGo, which will be used in this case, kinda sucks, and you'll have a lot of pain getting the two sides, OpenSSL and the go HTTP lib, to talk properly to eachother.
For me at least, I chose Go on a recent network project specifically because of the blessed, quality crypto impl for things I needed.
So the most widely supported platform for crypto libs would be C.
But C is probably not a good choice due to other factors outside crypto lib support.
I think the best implemented crypto lib out there atm is NaCl (djb). It has very few functions that take obvious parameters with which you can't blow your leg off (the only danger is repeating a nonce but generating a random nonce or sequential nonce is within the realm of "I expect most people to be able to read /dev/random".)
Second would be any crypto library that is implemented similar: few leg-blow-off-safe functions that do all the hard parts for you.