Mormot 1.18 (stable): https://github.com/synopse/mORMot/blob/master/SynCrtSock.pas
Mormot 2: https://github.com/synopse/mORMot2/blob/master/src/net/mormo...
https://synopse.info/files/html/api-1.18/SynCrtSock.html#THT...
https://synopse.info/files/html/Synopse%20mORMot%20Framework...
They have multiple client implementations. You can pick the one you like (THTTPClientSocket, TWinHTTP, TWinINET, TCurlHTTP, TWinHttpWebSocketClient).
If you want to write an oss ORM/SOA framework with HTTP, you cannot use a HTTP client library, because then people cannot compile your framework when they do not have the library installed. You can write in the documentation, they should install the library, but no one reads that. Also, if the library gets an update, it might not be compatible anymore.
So you need to bundle the HTTP client in your framework. Now you could write your own or fork one, but in either case you end up with a framework and its own HTTP client.