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).

--- a/src/http/modules/ngx_http_ssl_module.h
+++ b/src/http/modules/ngx_http_ssl_module.h
@@ -35,6 +35,7 @@ typedef struct {
     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;