mod_acme_alpn.c

#include "httpd.h"
#include "http_config.h"
#include "http_protocol.h"
#include <http_log.h>
#include "ap_config.h"

#define AP_PROTOCOL_ACME_ALPN "acme/tls-1"

static int acme_alpn_protocol_propose(conn_rec *c, request_rec *r,
                               server_rec *s,
                               const apr_array_header_t *offers,
                               apr_array_header_t *proposals)
{
  ap_log_cerror(APLOG_MARK, APLOG_TRACE1, 0, c, "In protocol_propose");
  if (!offers)
  {
    return DECLINED;
  }
  const char *offer = AP_PROTOCOL_ACME_ALPN;
  if (ap_array_str_contains(offers, offer))
  {
    ap_log_cerror(APLOG_MARK, APLOG_TRACE1, 0, c, "protocol_propose: Proposing %s", offer);    
    APR_ARRAY_PUSH(proposals, const char*) = offer;
    return OK;
  }
  return DECLINED;
}

static int acme_alpn_protocol_switch(conn_rec *c, request_rec *r, server_rec *s,
                              const char *protocol)
{
  ap_log_cerror(APLOG_MARK, APLOG_TRACE1, 0, c, "In protocol_switch");  
  /* Can't override the ServerHello lol! */
  return OK;  
}

static const char *acme_alpn_protocol_get(const conn_rec *c)
{
  ap_log_cerror(APLOG_MARK, APLOG_TRACE1, 0, c, "In protocol_get: NULL");
  return NULL;
}

void acme_alpn_register_hooks(apr_pool_t *pool)
{
  ap_hook_protocol_propose(acme_alpn_protocol_propose, NULL, NULL, APR_HOOK_MIDDLE);
  ap_hook_protocol_switch(acme_alpn_protocol_switch, NULL, NULL, APR_HOOK_MIDDLE);
  ap_hook_protocol_get(acme_alpn_protocol_get, NULL, NULL, APR_HOOK_MIDDLE);
}

module AP_MODULE_DECLARE_DATA acme_alpn_module =
{ 
    STANDARD20_MODULE_STUFF,
    NULL, /* Per-directory configuration handler */
    NULL,  /* Merge handler for per-directory configurations */
    NULL, /* Per-server configuration handler */
    NULL,  /* Merge handler for per-server configurations */
    NULL,      /* Any directives we may have for httpd */
    acme_alpn_register_hooks   /* Our hook registering function */
};

I found your httpd module in the forum and wanted to test it out. https://community.letsencrypt.org/t/so-how-are-we-bringing-tls-alpn-to-the-masses/63824

I looked at the code of your module and the implementaton of the http2 module. I wondered why it's not working. The cause was the wrong protocol name. acme/tls-1 should be acme-tls/1.

In my fork I created a docker test environment.

My successfull tests https://gist.github.com/dol/519f98d7c0d45d5b210f8753c05cf8b4#file-serverhello-png return acme-tls/1 in the ServerHello.