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update_certs_pem() replaced the certificate, key and client CAs inside the TLS context while handshakes on other threads were still reading them, and only the creation of a session was serialized with it. A server rotating its certificates under load could crash. Count the handshakes in progress, make an update wait until there are none, and hold off new handshakes while an update is pending so that a steady stream of them cannot keep it waiting. The wait is bounded by the handshake timeout.
79 lines
2.5 KiB
Markdown
79 lines
2.5 KiB
Markdown
---
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title: "T03. Start an SSL/TLS Server"
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order: 45
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status: "draft"
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---
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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`.
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## Basic usage
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```cpp
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#define CPPHTTPLIB_OPENSSL_SUPPORT
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#include <httplib.h>
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int main() {
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httplib::SSLServer svr("cert.pem", "key.pem");
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svr.Get("/", [](const auto &req, auto &res) {
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res.set_content("hello over TLS", "text/plain");
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});
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svr.listen("0.0.0.0", 443);
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}
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```
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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`.
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## Password-protected private keys
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The fifth argument is the private key password.
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```cpp
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httplib::SSLServer svr("cert.pem", "key.pem",
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nullptr, nullptr, "password");
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```
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The third and fourth arguments are for client certificate verification (mTLS, see [T04. Configure mTLS](../t04-mtls)). For now, pass `nullptr`.
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## Load PEM data from memory
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When you want to load certs from memory instead of files, use the `PemMemory` struct.
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```cpp
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httplib::SSLServer::PemMemory pem{};
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pem.cert_pem = cert_data.data();
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pem.cert_pem_len = cert_data.size();
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pem.key_pem = key_data.data();
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pem.key_pem_len = key_data.size();
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httplib::SSLServer svr(pem);
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```
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Handy when you pull certificates from environment variables or a secrets manager.
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## Rotate certificates
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Before a certificate expires, you may want to swap it out without restarting the server. That's what `update_certs_pem()` is for.
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```cpp
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svr.update_certs_pem(new_cert_pem, new_key_pem);
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```
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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.
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## Generating a test certificate
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For a throwaway self-signed cert, use the `openssl` CLI.
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```sh
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openssl req -x509 -newkey rsa:2048 -days 365 -nodes \
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-keyout key.pem -out cert.pem -subj "/CN=localhost"
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```
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In production, use certificates from Let's Encrypt or your internal CA.
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> **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).
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> For mutual TLS (client certificates), see [T04. Configure mTLS](../t04-mtls).
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