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title: “HTTPS Server” draft: true order: 7

In the previous chapter, you used an HTTPS client. Now let's set up your own HTTPS server. Just swap httplib::Server from Chapter 3 with httplib::SSLServer.

A TLS server needs a server certificate and a private key, though. Let's get those ready first.

Creating a Self-Signed Certificate

For development and testing, a self-signed certificate works just fine. You can generate one quickly with an OpenSSL command.

openssl req -x509 -noenc -keyout key.pem -out cert.pem -subj /CN=localhost

This creates two files:

• cert.pem — Server certificate
• key.pem — Private key

A Minimal HTTPS Server

Once you have your certificate, let's write the server.

#define CPPHTTPLIB_OPENSSL_SUPPORT
#include "httplib.h"
#include <iostream>

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

    svr.Get("/", [](const auto &, auto &res) {
        res.set_content("Hello, HTTPS!", "text/plain");
    });

    std::cout << "Listening on https://localhost:8443" << std::endl;
    svr.listen("0.0.0.0", 8443);
}

Just pass the certificate and private key paths to the httplib::SSLServer constructor. The routing API is exactly the same as httplib::Server from Chapter 3.

Compile and start it up.

Testing It Out

With the server running, try accessing it with curl. Since we're using a self-signed certificate, add the -k option to skip certificate verification.

curl -k https://localhost:8443/
# Hello, HTTPS!

If you open https://localhost:8443 in a browser, you‘ll see a “This connection is not secure” warning. That’s expected with a self-signed certificate. Just proceed past it.

Connecting from a Client

Let's connect using httplib::Client from the previous chapter. There are two ways to connect to a server with a self-signed certificate.

Option 1: Disable Certificate Verification

This is the quick and easy approach for development.

#define CPPHTTPLIB_OPENSSL_SUPPORT
#include "httplib.h"
#include <iostream>

int main() {
    httplib::Client cli("https://localhost:8443");
    cli.enable_server_certificate_verification(false);

    auto res = cli.Get("/");
    if (res) {
        std::cout << res->body << std::endl;  // Hello, HTTPS!
    }
}

Option 2: Specify the Self-Signed Certificate as a CA Certificate

This is the safer approach. You tell the client to trust cert.pem as a CA certificate.

#define CPPHTTPLIB_OPENSSL_SUPPORT
#include "httplib.h"
#include <iostream>

int main() {
    httplib::Client cli("https://localhost:8443");
    cli.set_ca_cert_path("cert.pem");

    auto res = cli.Get("/");
    if (res) {
        std::cout << res->body << std::endl;  // Hello, HTTPS!
    }
}

This way, only connections to the server with that specific certificate are allowed, preventing impersonation. Use this approach whenever possible, even in test environments.

Comparing Server and SSLServer

The httplib::Server API you learned in Chapter 3 works exactly the same with httplib::SSLServer. The only difference is the constructor.

	httplib::Server	httplib::SSLServer
Constructor	No arguments	Certificate and private key paths
Protocol	HTTP	HTTPS
Port (convention)	8080	8443
Routing	Same	Same

To switch an HTTP server to HTTPS, just change the constructor.

Next Steps

Your HTTPS server is up and running. You now have the basics of both HTTP/HTTPS clients and servers covered.

Next, let's look at the WebSocket support that was recently added to cpp-httplib.

Next: WebSocket