Verify Expect: 100-Continue header on POST or PUT requests
We may be adding support for the 100-Continue header in order to successfully upload content on some member node servers.
More description of the header's use from a Java client:
'Expect: 100-Continue' handshake for the entity enclosing methods. The purpose of the Expect: 100-Continue handshake is to allow the client that is sending a request message with a request body to determine if the origin server is willing to accept the request (based on the request headers) before the client sends the request body. The use of the Expect: 100-continue handshake can result in a noticeable performance improvement for entity enclosing requests (such as POST and PUT) that require the target server's authentication. https://hc.apache.org/httpcomponents-client-4.2.x/tutorial/html/fundamentals.html