Indy, mORMot2, FPHttpServer - each of them works on both Linux and Windows without any problems, each of them supports OpenSSL (indy only 1.02 - out of the box, fphttpserver only 1.1 for FPC 3.2.2 - in FPC fixes and trunk also 3.0, mORMot: 1.1., 3.0, 3.1) and none of them has problems with UTF-8.
A simple example is attached