it may use 'REST api ' but it depends what you mean by 'connectivity'. Authentication and Authorization - these are separate and this is what you're asking for I believe.
You need to determine what authentication mechanism is used by the Elastic service to enable the forum members to provide guidance on setting up the authentication.
if this helped answer the post, could you please mark it as 'solved'? Also if you consider whether the title of your post is relevant? Perhaps if the post is solved, it might make sense to update the Subject header field of the post to something more descriptive? This will help people when searching for problems. Ta