End the bootstrap mode once the standing dialog is initialized

fints/client.py

@@ -1273,6 +1273,14 @@ def __init__(self, bank_identifier, user_id, pin, server, customer_id=None, tan_
         self._bootstrap_mode = True
         super().__init__(bank_identifier=bank_identifier, user_id=user_id, customer_id=customer_id, *args, **kwargs)
 
+    def __enter__(self):
+        retval = super().__enter__()
+        # The bootstrap (fetch_tan_mechanisms(), get_tan_media()) is done
+        # without a standing dialog: errors like 9075 are not expected anymore
+        # once the standing dialog has been initialized
+        self._bootstrap_mode = False
+        return retval
+
     def _new_dialog(self, lazy_init=False):
         if self.pin is None:
             enc = None

tests/conftest.py

@@ -50,6 +50,18 @@ def make_answer(self, dialog_id, message):
 
             result = []
 
+            hkidn_user = re.search(rb"'HKIDN:\d+:2\+280:12345678\+([^+]+)\+", message)
+            if hkidn_user:
+                datadict['user'] = hkidn_user.group(1)
+
+            # Some banks require a strong customer authentication for fetching
+            # the transactions
+            hkkaz_sca = re.search(rb"'HKKAZ:(\d+):\d+\+", message)
+            if hkkaz_sca and datadict.get('user') == b'test-sca':
+                result.append(b"HIRMG::2+9050::Nachricht teilweise fehlerhaft.'")
+                result.append("HIRMS::2:{}+9075::Starke Authentifizierung erforderlich.'".format(hkkaz_sca.group(1).decode('us-ascii')).encode('us-ascii'))
+                return b"".join(result)
+
             result.append(b"HIRMG::2+0010::Nachricht entgegengenommen'")
 
             hkvvb = re.search(rb"'HKVVB:(\d+):3\+(\d+)\+(\d+)", message)

tests/test_client.py

@@ -1,5 +1,6 @@
 from fints.client import FinTS3PinTanClient, TransactionResponse, NeedTANResponse, ResponseStatus, NeedRetryResponse
-from fints.exceptions import FinTSClientPINError, FinTSClientTemporaryAuthError
+from fints.exceptions import FinTSClientPINError, FinTSClientTemporaryAuthError, FinTSSCARequiredError
+from datetime import date
 from decimal import Decimal
 import pytest
 
@@ -29,6 +30,22 @@ def test_get_information(fints_client):
     assert information["bank"]["name"] == 'Test Bank'
 
 
+def test_sca_required(fints_server):
+    """A 9075 response to a command raises FinTSSCARequiredError, also for a
+    client that never called get_tan_media()"""
+    client = FinTS3PinTanClient(
+        '12345678',
+        'test-sca',
+        '1234',
+        fints_server,
+        product_id="TEST-123", product_version="1.2.3",
+    )
+    with pytest.raises(FinTSSCARequiredError):
+        with client:
+            accounts = client.get_sepa_accounts()
+            client.get_transactions(accounts[0], date(2026, 10, 1), date(2026, 10, 2))
+
+
 def test_pin_wrong(fints_server):
     client = FinTS3PinTanClient(
         '12345678',