Add getEkm

Summary: To generically get the exported keying material from our transports. As the code comments say this is intended to be used to bind data to the stream/connection itself.

Reviewed By: yfeldblum, knekritz

Differential Revision: D33828649

fbshipit-source-id: c046eccfad5fc34188a310409ceb6c84d42e9f79

folly/io/async/AsyncTransport.h

@@ -807,6 +807,20 @@ class AsyncTransport : public DelayedDestruction,
    */
   virtual std::string getSecurityProtocol() const { return ""; }
 
+  /*
+   * A transport may be able to produce exported keying material (ekm, per
+   * rfc5705), that can be used to bind some arbitrary data to it. This can be
+   * useful in contexts where you may want a token to only be used on the
+   * transport it was created for. If the transport is incapable of producing
+   * the ekm, this should return nullptr.
+   */
+  virtual std::unique_ptr<IOBuf> getExportedKeyingMaterial(
+      folly::StringPiece /* label */,
+      std::unique_ptr<IOBuf> /* context */,
+      uint16_t /* length */) const {
+    return nullptr;
+  }
+
   /**
    * @return True iff end of record tracking is enabled
    */

folly/io/async/DecoratedAsyncTransportWrapper.h

@@ -154,6 +154,14 @@ class DecoratedAsyncTransportWrapper : public folly::AsyncTransport {
     return transport_->getSecurityProtocol();
   }
 
+  std::unique_ptr<IOBuf> getExportedKeyingMaterial(
+      folly::StringPiece label,
+      std::unique_ptr<IOBuf> context,
+      uint16_t length) const override {
+    return transport_->getExportedKeyingMaterial(
+        label, std::move(context), length);
+  }
+
   bool isReplaySafe() const override { return transport_->isReplaySafe(); }
 
   void setReplaySafetyCallback(