There are some tests set out in law to determine if someone legitimately holdsa religious belief, these tests primarily come from courts having to decide if someone claiming to be a conscientious objector legitimately holds a religious belief or is just trying to get out of going to war.
The tests relate to whether the beliefs are recognized by a community, the individual having a history of participation, etc.
So you can't just make up crazy claims, the courts will validate trust the beliefs are consistent with a religious community you are known to be active in.
What the court WON'T do is debate the Koran. If your religious community wears the niqab, and your participation in that community is clear, the court will accept you have a religious belief.
It also depends on the circumstances in which the issue arises. A sikh claiming a religious exception to keep his turban on will have to work harder in the court if he's trying to avoid wearing a motorcycle helmet, than if he wants to enter a restaurant that bars hats on men. We adjust the primacy of rights in accord with sensible and customary limitations that make society work. The rights always come first, then the limits and only as their need is proven. Once the Court ruled the law was against them not her, the Harper government offered not one single reason why Ms. Ishaq should be further prevented from taking her oath.
No one ever needed to see anyone's lips moving at a Citizenship ceremony. If in doubt all they had to do was stand next to them or ask them to say it again.
The least defensible reason to limit anyone's personal religious practice is to cite some outside religious authority as if they've been given the power to define and compel believers. That's called state religion and the next step is defining just one True Belief.
So
FAST, to answer your question, it's you who gets to decide if your beliefs are legit. We only get to limit them as we can prove there is some overriding need to. So if you've picked some wacko religion, we'll just snigger up our sleeves, but you'd better be ready to work as damn hard as every real believer — like Zunera Ishaq, and those sikhs and jews and Jehovah's Witnesses and Hindus and … — who fought for the right you toss off as if it was nothing. And thanks to folks like you, your fight will be hard and costly. Like theirs.
We can all be grateful your version of defining religious orthodoxy isn't as deadly as some, but it is the same.