The SSE Server Hub allows for HTTP Client Requests (through a Rest Expose API) to be persisted for Event Streaming as per protocol1. This is accomplished by switching the mime-type response to the appropriate text/event-stream and flushing the messages complying to the event source format2.
The SSE Client implements the Event Source JS Interface containing the Server Sent Event API, also per protocol3.
Effectively, no third parties are required for Server Push/Messaging.
Please refer to the Documentation tab for further details.
1 https://html.spec.whatwg.org/multipage/server-sent-events.html
2 https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events
3 https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events
A big thanks to several community members for pointing, suggesting and testing the above, its a huge help!