ssl: Add :getlocalchain() + :getlocalcertificate() to mirror the peer methods

These methods mirror the existing methods that fetch the peer certificate and
chain. Due to various factors (SNI, multiple key types, etc.) it is not always
trivial for an application to determine what certificate was presented to the
client. However there are various use-cases where this is needed, such as
tls-server-end-point channel binding and OCSP stapling.

Requires OpenSSL 1.0.2+ (note: SSL_get_certificate() has existed for a very
long time, but was lacking documentation until OpenSSL 3.0).

samples/chain/server.lua

@@ -31,8 +31,27 @@ util.show( conn:getpeercertificate() )
 
 print("----------------------------------------------------------------------")
 
-for k, cert in ipairs( conn:getpeerchain() ) do
+local expectedpeerchain = { "../certs/clientAcert.pem", "../certs/rootA.pem" }
+
+local peerchain = conn:getpeerchain()
+assert(#peerchain == #expectedpeerchain)
+for k, cert in ipairs( peerchain ) do
   util.show(cert)
+  local expectedpem = assert(io.open(expectedpeerchain[k])):read("*a")
+  assert(cert:pem() == expectedpem, "peer chain mismatch @ "..tostring(k))
+end
+
+local expectedlocalchain = { "../certs/serverAcert.pem" }
+
+local localchain = assert(conn:getlocalchain())
+assert(#localchain == #expectedlocalchain)
+for k, cert in ipairs( localchain ) do
+  util.show(cert)
+  local expectedpem = assert(io.open(expectedlocalchain[k])):read("*a")
+  assert(cert:pem() == expectedpem, "local chain mismatch @ "..tostring(k))
+  if k == 1 then
+    assert(cert:pem() == conn:getlocalcertificate():pem())
+  end
 end
 
 local f = io.open(params.certificate)

src/ssl.c

@@ -530,6 +530,58 @@ static int meth_getpeercertificate(lua_State *L)
   return 1;
 }
 
+/**
+ * Return the nth certificate of the chain sent to our peer.
+ */
+static int meth_getlocalcertificate(lua_State *L)
+{
+  int n;
+  X509 *cert;
+  STACK_OF(X509) *certs;
+  p_ssl ssl = (p_ssl)luaL_checkudata(L, 1, "SSL:Connection");
+  if (ssl->state != LSEC_STATE_CONNECTED) {
+    lua_pushnil(L);
+    lua_pushstring(L, "closed");
+    return 2;
+  }
+  /* Default to the first cert */
+  n = (int)luaL_optinteger(L, 2, 1);
+  /* This function is 1-based, but OpenSSL is 0-based */
+  --n;
+  if (n < 0) {
+    lua_pushnil(L);
+    lua_pushliteral(L, "invalid certificate index");
+    return 2;
+  }
+  if (n == 0) {
+    cert = SSL_get_certificate(ssl->ssl);
+    if (cert)
+      lsec_pushx509(L, cert);
+    else
+      lua_pushnil(L);
+    return 1;
+  }
+  /* In a server-context, the stack doesn't contain the peer cert,
+   * so adjust accordingly.
+   */
+  if (SSL_is_server(ssl->ssl))
+    --n;
+  if(SSL_get0_chain_certs(ssl->ssl, &certs) != 1) {
+    lua_pushnil(L);
+  } else {
+    if (n >= sk_X509_num(certs)) {
+      lua_pushnil(L);
+      return 1;
+    }
+    cert = sk_X509_value(certs, n);
+    /* Increment the reference counting of the object. */
+    /* See SSL_get_peer_certificate() source code.     */
+    X509_up_ref(cert);
+    lsec_pushx509(L, cert);
+  }
+  return 1;
+}
+
 /**
  * Return the chain of certificate of the peer.
  */
@@ -564,6 +616,41 @@ static int meth_getpeerchain(lua_State *L)
   return 1;
 }
 
+/**
+ * Return the chain of certificates sent to the peer.
+ */
+static int meth_getlocalchain(lua_State *L)
+{
+  int i;
+  int idx = 1;
+  int n_certs;
+  X509 *cert;
+  STACK_OF(X509) *certs;
+  p_ssl ssl = (p_ssl)luaL_checkudata(L, 1, "SSL:Connection");
+  if (ssl->state != LSEC_STATE_CONNECTED) {
+    lua_pushnil(L);
+    lua_pushstring(L, "closed");
+    return 2;
+  }
+  lua_newtable(L);
+  if (SSL_is_server(ssl->ssl)) {
+    lsec_pushx509(L, SSL_get_certificate(ssl->ssl));
+    lua_rawseti(L, -2, idx++);
+  }
+  if(SSL_get0_chain_certs(ssl->ssl, &certs)) {
+    n_certs = sk_X509_num(certs);
+    for (i = 0; i < n_certs; i++) {
+      cert = sk_X509_value(certs, i);
+      /* Increment the reference counting of the object. */
+      /* See SSL_get_peer_certificate() source code.     */
+      X509_up_ref(cert);
+      lsec_pushx509(L, cert);
+      lua_rawseti(L, -2, idx++);
+    }
+  }
+  return 1;
+}
+
 /**
  * Copy the table src to the table dst.
  */
@@ -908,7 +995,9 @@ static luaL_Reg methods[] = {
   {"getfd",               meth_getfd},
   {"getfinished",         meth_getfinished},
   {"getpeercertificate",  meth_getpeercertificate},
+  {"getlocalcertificate", meth_getlocalcertificate},
   {"getpeerchain",        meth_getpeerchain},
+  {"getlocalchain",       meth_getlocalchain},
   {"getpeerverification", meth_getpeerverification},
   {"getpeerfinished",     meth_getpeerfinished},
   {"exportkeyingmaterial",meth_exportkeyingmaterial},