Clear errors when reading pems

Summary: Clear/read OpenSSL errors after certain ops.

Reviewed By: mingtaoy

Differential Revision: D8277088

fbshipit-source-id: aa436657c3bca3a081cd56858e09da57a03cda05

folly/io/async/SSLContext.cpp

@@ -330,7 +330,7 @@ void SSLContext::loadTrustedCertificates(X509_STORE* store) {
 void SSLContext::loadClientCAList(const char* path) {
   auto clientCAs = SSL_load_client_CA_file(path);
   if (clientCAs == nullptr) {
-    LOG(ERROR) << "Unable to load ca file: " << path;
+    LOG(ERROR) << "Unable to load ca file: " << path << " " << getErrors();
     return;
   }
   SSL_CTX_set_client_CA_list(ctx_, clientCAs);

folly/ssl/OpenSSLCertUtils.cpp

@@ -209,6 +209,7 @@ std::vector<X509UniquePtr> OpenSSLCertUtils::readCertsFromBuffer(
   while (true) {
     X509UniquePtr x509(PEM_read_bio_X509(b.get(), nullptr, nullptr, nullptr));
     if (!x509) {
+      ERR_clear_error();
       break;
     }
     certs.push_back(std::move(x509));