The casino player account verification at online casinos is standard practice. The regulatory bodies make it a requirement that online casinos verify the identity of their players, which is partly to prevent fraud, underage gambling and money laundering.
At some point, the casino will ask you for documents to verify your identity and age. The request might come after account registration, after the deposit or before the withdrawal. Avoid needless cash out delays by providing the casino with requested documents ASAP. These may include a scan/copy of your passport or other government-issued ID. Provide proof of address by attaching a recent bank statement or utility bill.
Depending on the deposit payment method, the casino may also ask you for proof that the source of funds is in your name. For example, if you deposit using a credit card, provide a photo or scan of your credit card statement with sensitive information scratched out. Alternatively, if you use an e-wallet, provide a screenshot of your e-wallet account that clearly shows that you're the owner of the account.