[EXPORTER] OTLP GRPC mTLS support (open-telemetry#2120)

Author: kylepl

api/CMakeLists.txt

@@ -113,6 +113,11 @@ if(WITH_OTLP_HTTP_SSL_PREVIEW)
   endif()
 endif()
 
+if(WITH_OTLP_GRPC_SSL_MTLS_PREVIEW)
+  target_compile_definitions(opentelemetry_api
+                             INTERFACE ENABLE_OTLP_GRPC_SSL_MTLS_PREVIEW)
+endif()
+
 if(WITH_METRICS_EXEMPLAR_PREVIEW)
   target_compile_definitions(opentelemetry_api
                              INTERFACE ENABLE_METRICS_EXEMPLAR_PREVIEW)

ci/do_ci.sh

@@ -258,6 +258,7 @@ elif [[ "$1" == "cmake.exporter.otprotocol.test" ]]; then
   cmake -DCMAKE_BUILD_TYPE=Debug  \
         -DWITH_OTLP_GRPC=ON \
         -DWITH_OTLP_HTTP=ON \
+        -DWITH_OTLP_GRPC_SSL_MTLS_PREVIEW=ON \
         "${SRC_DIR}"
   grpc_cpp_plugin=`which grpc_cpp_plugin`
   proto_make_file="CMakeFiles/opentelemetry_proto.dir/build.make"

exporters/otlp/include/opentelemetry/exporters/otlp/otlp_grpc_exporter_options.h

@@ -28,6 +28,19 @@ struct OtlpGrpcExporterOptions
   // ssl_credentials_cacert_as_string in-memory string representation of .pem file to be used for
   // SSL encryption.
   std::string ssl_credentials_cacert_as_string = GetOtlpDefaultSslCertificateString();
+
+#ifdef ENABLE_OTLP_GRPC_SSL_MTLS_PREVIEW
+  // At most one of ssl_client_key_* should be non-empty. If use_ssl_credentials, they will
+  // be read to allow for mTLS.
+  std::string ssl_client_key_path   = GetOtlpDefaultTracesSslClientKeyPath();
+  std::string ssl_client_key_string = GetOtlpDefaultTracesSslClientKeyString();
+
+  // At most one of ssl_client_cert_* should be non-empty. If use_ssl_credentials, they will
+  // be read to allow for mTLS.
+  std::string ssl_client_cert_path   = GetOtlpDefaultTracesSslClientCertificatePath();
+  std::string ssl_client_cert_string = GetOtlpDefaultTracesSslClientCertificateString();
+#endif
+
   // Timeout for grpc deadline
   std::chrono::system_clock::duration timeout = GetOtlpDefaultTimeout();
   // Additional HTTP headers

exporters/otlp/src/otlp_grpc_client.cc

@@ -34,6 +34,18 @@ static std::string GetFileContents(const char *fpath)
   finstream.close();
   return contents;
 }
+
+// If the file path is non-empty, returns the contents of the file. Otherwise returns contents.
+static std::string GetFileContentsOrInMemoryContents(const std::string &file_path,
+                                                     const std::string &contents)
+{
+  if (!file_path.empty())
+  {
+    return GetFileContents(file_path.c_str());
+  }
+  return contents;
+}
+
 }  // namespace
 
 std::shared_ptr<grpc::Channel> OtlpGrpcClient::MakeChannel(const OtlpGrpcExporterOptions &options)
@@ -61,14 +73,14 @@ std::shared_ptr<grpc::Channel> OtlpGrpcClient::MakeChannel(const OtlpGrpcExporte
   if (options.use_ssl_credentials)
   {
     grpc::SslCredentialsOptions ssl_opts;
-    if (options.ssl_credentials_cacert_path.empty())
-    {
-      ssl_opts.pem_root_certs = options.ssl_credentials_cacert_as_string;
-    }
-    else
-    {
-      ssl_opts.pem_root_certs = GetFileContents((options.ssl_credentials_cacert_path).c_str());
-    }
+    ssl_opts.pem_root_certs = GetFileContentsOrInMemoryContents(
+        options.ssl_credentials_cacert_path, options.ssl_credentials_cacert_as_string);
+#if ENABLE_OTLP_GRPC_SSL_MTLS_PREVIEW
+    ssl_opts.pem_private_key = GetFileContentsOrInMemoryContents(options.ssl_client_key_path,
+                                                                 options.ssl_client_key_string);
+    ssl_opts.pem_cert_chain  = GetFileContentsOrInMemoryContents(options.ssl_client_cert_path,
+                                                                options.ssl_client_cert_string);
+#endif
     channel =
         grpc::CreateCustomChannel(grpc_target, grpc::SslCredentials(ssl_opts), grpc_arguments);
   }