The include_email is passed in the GET request. I’ve also tried to target https://api.twitter.com/1.1/account/verify_credentials.json?include_email=true as the API url, but still the same error.
Don’t know if this helps, but I’ve tried a different call for client:
return client.target( apiUrl )
.queryParam("include_email", true)
.request()
.header("Authorization", authHeader)
.get( Map.class );
and this time it gives HTTP 401 Authorization required error, although the Authorization header is correct.