Rework SCTP auth pipeline to allow dynamic key change

The SCTP key sharing mechanism won't be using a file to communicate
the active authentication key anymore as we will be receiving
it directly into message bridge through an AOS channel instead.

Change-Id: I46e079b98cbb6a0ed52fca36c67f7fa724ba249c
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/network/message_bridge_client.cc b/aos/network/message_bridge_client.cc
index afe2a90..82a59fb 100644
--- a/aos/network/message_bridge_client.cc
+++ b/aos/network/message_bridge_client.cc
@@ -9,12 +9,6 @@
 DEFINE_string(config, "aos_config.json", "Path to the config.");
 DEFINE_int32(rt_priority, -1, "If > 0, run as this RT priority");
 
-#if HAS_SCTP_AUTH
-DEFINE_string(sctp_auth_key_file, "",
-              "When set, use the provided key for SCTP authentication as "
-              "defined in RFC 4895. The file should be binary-encoded");
-#endif
-
 namespace aos {
 namespace message_bridge {
 
@@ -29,14 +23,7 @@
     event_loop.SetRuntimeRealtimePriority(FLAGS_rt_priority);
   }
 
-  std::vector<uint8_t> auth_key;
-#if HAS_SCTP_AUTH
-  if (!FLAGS_sctp_auth_key_file.empty()) {
-    auth_key = ReadFileToVecOrDie(FLAGS_sctp_auth_key_file);
-  }
-#endif
-  MessageBridgeClient app(&event_loop, Sha256(config.span()),
-                          std::move(auth_key));
+  MessageBridgeClient app(&event_loop, Sha256(config.span()));
 
   logging::DynamicLogging dynamic_logging(&event_loop);
   // TODO(austin): Save messages into a vector to be logged.  One file per