@Override
  public SSLEngineResult unwrap(ByteBuffer byteBuffer, ByteBuffer[] byteBuffers) throws SSLException {
    return delegateEngine.unwrap(byteBuffer, byteBuffers);
  }
@param delegateEngine An {@link SSLEngine} to delegate to in most cases.
@param sessionToReturn If not {@code null}, return this certificate in {@link #getSession()} instead of delegating.
ambry-test-utils/src/main/java/com/github/ambry/rest/MockSSLEngine.java