OCSP stapling: ssl_trusted_certificate directive.

The directive allows to specify additional trusted Certificate Authority
certificates to be used during certificate verification.  In contrast to
ssl_client_certificate DNs of these cerificates aren't sent to a client
during handshake.

Trusted certificates are loaded regardless of the fact whether client
certificates verification is enabled as the same certificates will be
used for OCSP stapling, during construction of an OCSP request and for
verification of an OCSP response.

The same applies to a CRL (which is now always loaded).
diff --git a/src/event/ngx_event_openssl.c b/src/event/ngx_event_openssl.c
index 5e25b01..5c45167 100644
--- a/src/event/ngx_event_openssl.c
+++ b/src/event/ngx_event_openssl.c
@@ -297,6 +297,33 @@
 
 
 ngx_int_t
+ngx_ssl_trusted_certificate(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *cert,
+    ngx_int_t depth)
+{
+    SSL_CTX_set_verify_depth(ssl->ctx, depth);
+
+    if (cert->len == 0) {
+        return NGX_OK;
+    }
+
+    if (ngx_conf_full_name(cf->cycle, cert, 1) != NGX_OK) {
+        return NGX_ERROR;
+    }
+
+    if (SSL_CTX_load_verify_locations(ssl->ctx, (char *) cert->data, NULL)
+        == 0)
+    {
+        ngx_ssl_error(NGX_LOG_EMERG, ssl->log, 0,
+                      "SSL_CTX_load_verify_locations(\"%s\") failed",
+                      cert->data);
+        return NGX_ERROR;
+    }
+
+    return NGX_OK;
+}
+
+
+ngx_int_t
 ngx_ssl_crl(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *crl)
 {
     X509_STORE   *store;
diff --git a/src/event/ngx_event_openssl.h b/src/event/ngx_event_openssl.h
index cd6d885..81f0a8b 100644
--- a/src/event/ngx_event_openssl.h
+++ b/src/event/ngx_event_openssl.h
@@ -101,6 +101,8 @@
     ngx_str_t *cert, ngx_str_t *key);
 ngx_int_t ngx_ssl_client_certificate(ngx_conf_t *cf, ngx_ssl_t *ssl,
     ngx_str_t *cert, ngx_int_t depth);
+ngx_int_t ngx_ssl_trusted_certificate(ngx_conf_t *cf, ngx_ssl_t *ssl,
+    ngx_str_t *cert, ngx_int_t depth);
 ngx_int_t ngx_ssl_crl(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *crl);
 RSA *ngx_ssl_rsa512_key_callback(SSL *ssl, int is_export, int key_length);
 ngx_int_t ngx_ssl_dhparam(ngx_conf_t *cf, ngx_ssl_t *ssl, ngx_str_t *file);
diff --git a/src/http/modules/ngx_http_ssl_module.c b/src/http/modules/ngx_http_ssl_module.c
index d759489..aa0a4b4 100644
--- a/src/http/modules/ngx_http_ssl_module.c
+++ b/src/http/modules/ngx_http_ssl_module.c
@@ -124,6 +124,13 @@
       offsetof(ngx_http_ssl_srv_conf_t, client_certificate),
       NULL },
 
+    { ngx_string("ssl_trusted_certificate"),
+      NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_CONF_TAKE1,
+      ngx_conf_set_str_slot,
+      NGX_HTTP_SRV_CONF_OFFSET,
+      offsetof(ngx_http_ssl_srv_conf_t, trusted_certificate),
+      NULL },
+
     { ngx_string("ssl_prefer_server_ciphers"),
       NGX_HTTP_MAIN_CONF|NGX_HTTP_SRV_CONF|NGX_CONF_FLAG,
       ngx_conf_set_flag_slot,
@@ -325,6 +332,7 @@
      *     sscf->dhparam = { 0, NULL };
      *     sscf->ecdh_curve = { 0, NULL };
      *     sscf->client_certificate = { 0, NULL };
+     *     sscf->trusted_certificate = { 0, NULL };
      *     sscf->crl = { 0, NULL };
      *     sscf->ciphers = { 0, NULL };
      *     sscf->shm_zone = NULL;
@@ -380,6 +388,8 @@
 
     ngx_conf_merge_str_value(conf->client_certificate, prev->client_certificate,
                          "");
+    ngx_conf_merge_str_value(conf->trusted_certificate,
+                         prev->trusted_certificate, "");
     ngx_conf_merge_str_value(conf->crl, prev->crl, "");
 
     ngx_conf_merge_str_value(conf->ecdh_curve, prev->ecdh_curve,
@@ -479,10 +489,18 @@
         {
             return NGX_CONF_ERROR;
         }
+    }
 
-        if (ngx_ssl_crl(cf, &conf->ssl, &conf->crl) != NGX_OK) {
-            return NGX_CONF_ERROR;
-        }
+    if (ngx_ssl_trusted_certificate(cf, &conf->ssl,
+                                    &conf->trusted_certificate,
+                                    conf->verify_depth)
+        != NGX_OK)
+    {
+        return NGX_CONF_ERROR;
+    }
+
+    if (ngx_ssl_crl(cf, &conf->ssl, &conf->crl) != NGX_OK) {
+        return NGX_CONF_ERROR;
     }
 
     if (conf->prefer_server_ciphers) {
diff --git a/src/http/modules/ngx_http_ssl_module.h b/src/http/modules/ngx_http_ssl_module.h
index 58659ab..1fb891b 100644
--- a/src/http/modules/ngx_http_ssl_module.h
+++ b/src/http/modules/ngx_http_ssl_module.h
@@ -35,6 +35,7 @@
     ngx_str_t                       dhparam;
     ngx_str_t                       ecdh_curve;
     ngx_str_t                       client_certificate;
+    ngx_str_t                       trusted_certificate;
     ngx_str_t                       crl;
 
     ngx_str_t                       ciphers;