cpp-httplib/docs-src/pages/en/cookbook/t03-ssl-server.md

title, order, status

title	order	status
T03. Start an SSL/TLS Server	44	draft

To stand up an HTTPS server, use httplib::SSLServer instead of httplib::Server. Pass a certificate and private key to the constructor, and you get back something that works exactly like Server.

Basic usage

#define CPPHTTPLIB_OPENSSL_SUPPORT
#include <httplib.h>

int main() {
  httplib::SSLServer svr("cert.pem", "key.pem");

  svr.Get("/", [](const auto &req, auto &res) {
    res.set_content("hello over TLS", "text/plain");
  });

  svr.listen("0.0.0.0", 443);
}

Pass the server certificate (PEM format) and private key file paths to the constructor. That's all you need for a TLS-enabled server. Registering handlers and calling listen() work the same as with Server.

Password-protected private keys

The fifth argument is the private key password.

httplib::SSLServer svr("cert.pem", "key.pem",
                       nullptr, nullptr, "password");

The third and fourth arguments are for client certificate verification (mTLS, see T04). For now, pass nullptr.

Load PEM data from memory

When you want to load certs from memory instead of files, use the PemMemory struct.

httplib::SSLServer::PemMemory pem{};
pem.cert_pem = cert_data.data();
pem.cert_pem_len = cert_data.size();
pem.key_pem = key_data.data();
pem.key_pem_len = key_data.size();

httplib::SSLServer svr(pem);

Handy when you pull certificates from environment variables or a secrets manager.

Rotate certificates

Before a certificate expires, you may want to swap it out without restarting the server. That's what update_certs_pem() is for.

svr.update_certs_pem(new_cert_pem, new_key_pem);

Existing connections keep using the old cert; new connections use the new one.

Generating a test certificate

For a throwaway self-signed cert, use the openssl CLI.

openssl req -x509 -newkey rsa:2048 -days 365 -nodes \
  -keyout key.pem -out cert.pem -subj "/CN=localhost"

In production, use certificates from Let's Encrypt or your internal CA.

Warning: Binding an HTTPS server to port 443 requires root. For a safe way to do that, see the privilege-drop pattern in S18. Control Startup Order with listen_after_bind.

For mutual TLS (client certificates), see T04. Configure mTLS.