Problem

The gateway is sending Expect: 100-continue to HTTP/1.1 servers and this behavior is not desired because there's no outbound authentication that could fail and therefore no reason not to send the body immediately.

Resolution

To disable Expect: 100-continue on all outbound connections globally, you can set the following property inside the ConfigurationFragment tags of your JVM settings file:

<VMArg name="-Ddont.expect.100.continue=true"/>

Note that this setting is global and there's no way to set this only for particular backends. It normally is not a problem to set this globally because all this does for most connections is to remove an unnecessary round-trip, it's trading off a possibility of using extra bandwidth for better latency, turning it off will not make connections fail. Note that the setting does not apply when BASIC authentication or Kerberos credentials are used via a credential profile. For more information on where and how to set JVM properties like this one, please refer to the documentation on system property changes.