---
title: "T03. Start an SSL/TLS Server"
order: 45
status: "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

```cpp
#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.

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

The third and fourth arguments are for client certificate verification (mTLS, see [T04. Configure mTLS](../t04-mtls)). For now, pass `nullptr`.

## Load PEM data from memory

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

```cpp
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.

```cpp
svr.update_certs_pem(new_cert_pem, new_key_pem);
```

Existing connections keep using the old cert; new connections use the new one. It waits for handshakes in progress to finish, at most the read timeout, and new connections wait until it returns. So don't call it from a TLS callback that runs during a handshake: it would wait for that handshake.

## Generating a test certificate

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

```sh
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`](../s18-listen-after-bind).

> For mutual TLS (client certificates), see [T04. Configure mTLS](../t04-mtls).