What is point of maximum authorized capital if shares can exceed par value on IPO day?

My question is, let's say a company has an Authorized Capital of $1000. Let's say they issue 50 shares with a par value of $10. So, they are raising $500 total. But let's say, on IPO day, the shares sell for $100. So, they raise $5000. But, their paid up capital was only $500. But they raised $5000. So what happens to that extra $4500? Is that money that the current owners can just pocket instead of going to the companies equity in the balance sheet? And what is the point of having a maximum authorized capital and a par value in the first place if, on IPO day, the initial price of the stock can be so much higher than the par value?