delegate RSA verify to the RSA module

src/tls_builtin.c

@@ -1704,7 +1704,6 @@ static int mg_tls_verify_cert_signature(const struct mg_tls_cert *cert,
       return 0;
     }
   } else {
-    uint8_t r;
     const uint8_t *n;
     size_t nlen;
     uint8_t sig2[512];  // 4096 bits
@@ -1724,15 +1723,7 @@ static int mg_tls_verify_cert_signature(const struct mg_tls_cert *cert,
       return 0;
     }
 
-    r = 0;
-    {
-      const uint8_t *p, *q;
-      size_t i;
-      p = sig2 + nlen - cert->tbshashsz;
-      q = cert->tbshash;
-      for (i = 0; i < cert->tbshashsz; i++) r |= (uint8_t)(*p++ ^ *q++);
-    }
-    return r == 0;
+    return mg_rsa_pkcs_verify(sig2, nlen, cert->tbshash, cert->tbshashsz);
   }
 }