If you don't know your values and beliefs, being authentic is difficult because authenticity requires acting in alignment with your core principles, which you can't do if you haven't identified those principles; essentially, you can't be true to yourself if you haven't figured out who "yourself" truly is at a deeper level.
The solution is to start looking closer at yourself and making a list of what you believe. At a fundamental level, most people have values. So, make a list of your values.
Honesty is a core value; even those who choose to be dishonest want others to be honest with them. A person may believe that no one is honest, but they still can conclude that it would be better if at least others were.
Accountability and gaining knowledge are core values; most people want others to be accountable for their actions and to continue to learn. If you agree, add that to the list.
Making a list is the first step, but if you look at your decisions and challenges and evaluate if they will help you stay consistent with your identified values, then other values will occur to you. For example, consider whether your career enables you to gain more knowledge and conclude that career reliance is your core value.
Core values are the fundamental beliefs that guide your actions and decisions. They help you stay true to yourself and how you want to show up in the world.