With the recent introduction of lokad ID indexing in chronik, this diff proposes a paywall lokad ID prefix (70617977 / PAYW) to accompany paywall payment transactions.
A typical payload will consist of:
> [OP_Return] [PAYW] [TXID of the paywalled article]
This simplified payload is on the basis that the txid of this paywall payment itself will contain the `XEC payment amount`, `payer address`, `payee address` and `payment date/time`, whilst the txid of the paywalled article can be used to derive (from onchain or offhcain sources) the requisite attributes of the article such as article title, content, author, date/time and the designated paywall price.
From a web app POV, it would just be a matter of:
1. Upon startup, calling Chronik to return all transactions matching the `PAYW` lokad ID
2. Caching the JSON response from Chronik
3. From the paywall checking callsite, check the recency of the cached paywall payments array before parsing to see whether a particular user address has successfully paid the correct amount to get past the paywall.