example_api.java

class SignUpRequest {
   String firstName;
   String lastName;
   String pin;
   List<Identifier> identifiers;
}

class Identifier {
  String identifier;
  String identifierType;
  
  public Identifier(identifier String, identifierType String) {
    this.identifier = identifier;
    this.identifierType = identifierType;
  }
}

public SignUpRequest createSignupRequest(String firstName, String lastName, String pin, String identifier) {
  SignUpRequest req = new SignUpRequest();
  req.firstName = firstName;
  req.lastName = lastName;
  req.pin = pin;
  req.identifiers = new ArrayList();
  req.identifiers.add(new Identifier(identifier, "email"));
  
  return req;
}