This is similar to guarantees and funding sources for loans, but for current accounts.
If an authorized / locked amount would be debited from a current account, this transaction would have accounting and (overdraft) interest calculation implications. This is not desired as the transactions are not yet effective.
a) New transaction state inside the transaction lifecycle:
The current transaction lifecycle of 1) "applied", 2) "reversed" and upcoming in APP-136 "Transaction States" 3) "pending approval" could be further extended by adding 4) "authorized" / (or "locked" or "frozen"). A valid transaction lifecycle would then go from: (optional) pending approval -> (optional) authorized -> applied -> (optional) reversed.
b) New transaction type:
A new transaction type "authorization" (or "lock" or "freeze") could be introduced. If an authorization becomes effective, is cleared or expires, it would be reversed and in case of effectiveness a withdrawal transaction is posted.