registerUser(user) {
  console.log(user);

  let headers = new Headers({ 'Content-Type': 'application/json' });
  let options = new RequestOptions({ headers: headers });

  return this.http.post(this.domain + 'authentication/register',
  JSON.stringify(user), options).map(res => res.json());
}

{
  address: "124124124"

  avatar: File {name: "big_5ae4786f899b2c8bf63b3ee481f0daf2503e402b.jpg",
  lastModified: 1503854933277, lastModifiedDate: Sun Aug 27 2017 20:28:53
  GMT+0300 (RTZ 2 (зима)), webkitRelativePath: "", size: 436719, …}

  birthday: {day:"1",month:"January",year:"1967"}
  email: "denisod93@gmail.com"
  password: "kamekadZ227@"
  phone: "123123412"
  username: "Denis"
}

router.post('/register', upload.any(), (req, res) => {
 console.log(req.body);
)};

{
  address: "124124124"

  avatar: {}

  birthday: {day:"1",month:"January",year:"1967"}
  email: "denisod93@gmail.com"
  password: "kamekadZ227@"
  phone: "123123412"
  username: "Denis"
}