Chitty27 helped with some details and he’s more:
(1) Web API to create a wallet: you can reference Counterwallet source (e.g. see https://github.com/CounterpartyXCP/counterwallet/blob/master/src/js/components/wallet.js). Here on forum you can see a simple wallet creation process in the code of Counterwallet Helper.
(2) You can get dummy XCP by getting BTC at a faucet and then once they’re at your address click on BTC and “Burn” and you’ll get testnet XCPs in return (this emulates the way XCPs were originally created, by burning BTC for XCP).
More here: How do I get XCP on Counterparty testnet?
Tokenly which Chitty27 mentioned has some of their PHP-based source on Github as well.