alts: fix server hang

Followup to #5893 which causes a server side hang. This is a hack.

alts/src/main/java/io/grpc/alts/internal/AltsProtocolNegotiator.java

@@ -34,9 +34,12 @@ import io.grpc.internal.ObjectPool;
 import io.grpc.netty.GrpcHttp2ConnectionHandler;
 import io.grpc.netty.InternalNettyChannelBuilder;
 import io.grpc.netty.InternalNettyChannelBuilder.ProtocolNegotiatorFactory;
+import io.grpc.netty.InternalProtocolNegotiationEvent;
 import io.grpc.netty.InternalProtocolNegotiator.ProtocolNegotiator;
 import io.grpc.netty.InternalProtocolNegotiators;
 import io.netty.channel.ChannelHandler;
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.handler.ssl.SslContext;
 import io.netty.util.AsciiString;
 import java.security.GeneralSecurityException;
@@ -163,7 +166,26 @@ public final class AltsProtocolNegotiator {
       ChannelHandler thh =
           new TsiHandshakeHandler(gnh, nettyHandshaker, new AltsHandshakeValidator());
       ChannelHandler wuah = InternalProtocolNegotiators.waitUntilActiveHandler(thh);
-      return wuah;
+      ChannelHandler knh = new KickNegotiationHandler(wuah);
+      return knh;
+    }
+
+    /** Kicks off negotiation of the server.  This is a hack workaround until server uses WBAEH.*/
+    // TODO(carl-mastrangelo): remove this once NettyServerTransport uses WBAEH.
+    private static final class KickNegotiationHandler extends ChannelInboundHandlerAdapter {
+
+      private final ChannelHandler next;
+
+      KickNegotiationHandler(ChannelHandler next) {
+        this.next = checkNotNull(next, "next");
+      }
+
+      @Override
+      public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
+        super.handlerAdded(ctx);
+        ctx.pipeline().replace(ctx.name(), /*newName= */ null, next);
+        ctx.pipeline().fireUserEventTriggered(InternalProtocolNegotiationEvent.getDefault());
+      }
     }
 
     @Override

alts/src/test/java/io/grpc/alts/internal/AltsProtocolNegotiatorTest.java

@@ -36,7 +36,6 @@ import io.grpc.internal.FixedObjectPool;
 import io.grpc.internal.GrpcAttributes;
 import io.grpc.internal.ObjectPool;
 import io.grpc.netty.GrpcHttp2ConnectionHandler;
-import io.grpc.netty.InternalProtocolNegotiationEvent;
 import io.grpc.netty.NettyChannelBuilder;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.ByteBufAllocator;
@@ -150,7 +149,6 @@ public class AltsProtocolNegotiatorTest {
         new AltsProtocolNegotiator.ServerAltsProtocolNegotiator(handshakerFactory, lazyFakeChannel)
             .newHandler(grpcHandler);
     channel = new EmbeddedChannel(uncaughtExceptionHandler, handler);
-    channel.pipeline().fireUserEventTriggered(InternalProtocolNegotiationEvent.getDefault());
   }
 
   @After