code: public Member enroll(String name, String secret) throws EnrollmentException {
          Member member = getMember(name);
          member.enroll(secret);
          members.put(name, member);
  
          return member;
      }
docs: Enroll a user or other identity which has already been registered.
  @param name The name of the user or other member to enroll.
  @param secret The enrollment secret of the user or other member to enroll.
  @throws EnrollmentException