The engine is open source, so with enough technical experience you could integrate anything really. However, there are currently a lot of apis that people integrate all the time with UE4. A popular one is steam. Each one will take a different amount of work. If you look at the engine source in visual studio, under the ThirdParty folders you can see what APIs come pre-bundled in the engine, and you can see its integration.
heres the article on steam integration to maybe give you an idea of how it all works:
EDIT:
here’s a good question asked on the answerhub on bringing in a third party api to UE4. Its not twitter, but it may also be useful in getting you traveling down the right road.