[Mint] Fix key rotation (#177)

* rotate keys every 5 seconds

* every 10 seconds

* do not regenerate all past keys for each epoch cycle

* remove automatic rotation

* make format

* print to logger

* rephrase print

cashu/mint/startup.py

@@ -1,6 +1,7 @@
 # startup routine of the standalone app. These are the steps that need
 # to be taken by external apps importing the cashu mint.
 
+import asyncio
 import importlib
 
 from loguru import logger
@@ -28,6 +29,20 @@ ledger = Ledger(
 )
 
 
+async def rotate_keys(n_seconds=10):
+    """Rotate keyset epoch every n_seconds.
+    Note: This is just a helper function for testing purposes.
+    """
+    i = 0
+    while True:
+        i += 1
+        logger.info("Rotating keys.")
+        ledger.derivation_path = f"0/0/0/{i}"
+        await ledger.init_keysets()
+        logger.info(f"Current keyset: {ledger.keyset.id}")
+        await asyncio.sleep(n_seconds)
+
+
 async def start_mint_init():
     await migrate_databases(ledger.db, migrations)
     await ledger.load_used_proofs()
@@ -45,3 +60,4 @@ async def start_mint_init():
 
     logger.info(f"Data dir: {settings.cashu_dir}")
     logger.info("Mint started.")
+    # asyncio.create_task(rotate_keys())