auth_identity: include openssl/x509_vfy.h

- looks like being required by openssl 1.1.0 to get the definition of
  X509_STORE_CTX
- reported by Victor Seva, GH #685

modules/auth_identity/auth_crypt.c

@@ -35,6 +35,7 @@
 #include <openssl/sha.h>
 #include <openssl/x509.h>
 #include <openssl/x509v3.h>
+#include <openssl/x509_vfy.h>
 
 #include "../../mem/mem.h"
 #include "../../parser/parse_uri.h"