tls-alpn-01 docs update for newer node versions

[mscdex]

Since node v20.18.0 and v22.9.0 and newer, you no longer need nginx/haproxy in front in order to do tls-alpn-01 issuance/renewal. Starting with these node versions, you can set the key and certificate for a connection inside the ALPNCallback in the https server config object, which allows you to do the tls-alpn-01 validation completely within node. Example:

let sslRenew = null;

// First define the `ALPNCallback` in your HTTPS server config
const httpsServer = https.createServer({
  // ...
  ALPNCallback: function({ servername, protocols }) {
    if (!Array.isArray(protocols))
      return;
    let http10;
    let http11;
    let acme;
    for (const protocol of protocols) {
      switch (protocol) {
        case 'http/1.0':
          http10 = protocol;
          break;
        case 'http/1.1':
          http11 = protocol;
          break;
        case 'acme-tls/1':
          acme = protocol;
          break;
      }
    }
    if (acme && sslRenew?.type === 'tls-alpn-01') {
      this.setKeyCert(sslRenew.ctx);
      return acme;
    }
    return http11 || http10 || undefined;
  },
});

// Then somewhere else where you are requesting a new certificate
// via `auto()`:
async function renewCert() {
  // ...
  const cert = await client.auto({
    // ...
    challengeCreateFn: async (authz, challenge, keyAuthorization) => {
      const type = challenge.type;
      switch (type) {
        case 'http-01':
          // Handling http-01 is outside the scope of this example
          sslRenew = {
            type,
            url: `/.well-known/acme-challenge/${challenge.token}`,
            data: keyAuthorization,
          };
          break;
        case 'tls-alpn-01': {
          const [ alpnKey, alpnCert ] =
            await acme.crypto.createAlpnCertificate(
              authz,
              keyAuthorization
            );
          sslRenew = {
            type,
            ctx: tls.createSecureContext({
              key: alpnKey,
              cert: alpnCert,
              minVersion: 'TLSv1.2',
            }),
          };
          break;
        }
      }
    },
    challengeRemoveFn: (authz) => {
      sslRenew = null;
    },
  });

  // Store key and obtained cert somewhere ...

  // Update the HTTPS server to use them ...
  httpsServer.setSecureContext({
    key,
    cert,
    minVersion: 'TLSv1.2',
  });
}