A pull request for this issue has been created at https://git.magnolia-cms.com/projects/MODULES/repos/publishing/pull-requests/114/overview

 
info.magnolia.publishing.sender.http.HttpClientProvider was recently added to the code base. It is used to create an Apache HttpClient for the respective ReceiverDefinition.

While this is a welcomed addition, it is not configurable, since it is privately instantiated in info.magnolia.publishing.sender.AbstractSender
 
We have several public instances, which require different proxy settings on the HttpClient.
 
Previously, we extended HttpCommitOperation and HttpRollbackOperation (which get instantiated by the Sender), while this is still somewhat possible, the public visible constructors are now Deprecated - effectively rendering our solution a dead end.
 
Please make the HttpClientProvider properly injectable - this would allow us to override the component.

Fixing this issue globally in the Sender seems to be the most reasonable and universally applicable approach.