1 files changed, 106 insertions, 0 deletions
diff --git a/postgresqleu/plaid/views.py b/postgresqleu/plaid/views.py
new file mode 100644
index 00000000..aa16766e
--- /dev/null
+++ b/postgresqleu/plaid/views.py
@@ -0,0 +1,106 @@
+from django.http import Http404, HttpResponse
+from django.shortcuts import get_object_or_404
+from django.views.decorators.csrf import csrf_exempt
+
+from cryptography.hazmat.primitives.asymmetric.ec import SECP256R1
+from cryptography.hazmat.primitives.asymmetric.ec import EllipticCurvePublicNumbers
+import hashlib
+import hmac
+import json
+import jwt
+import time
+
+from postgresqleu.invoices.models import InvoicePaymentMethod
+from postgresqleu.scheduler.util import trigger_immediate_job_run
+from postgresqleu.plaid.models import PlaidWebhookData
+
+
+def _validate_signature(request, method):
+    signed_jwt = request.META.get('HTTP_PLAID_VERIFICATION', '')
+    current_key_id = jwt.get_unverified_header(signed_jwt)['kid']
+
+    impl = method.get_implementation()
+    key = impl.get_signing_key(current_key_id)
+    if not key:
+        print("Signing key {} not found".format(current_key_id))
+        return False
+
+    if key.get('expired_at', None) is not None:
+        print("Key expired")
+        return False
+
+    if key['kty'] != 'EC' or key['alg'] != 'ES256' or key['crv'] != 'P-256':
+        print("Unknown type of key")
+        return False
+
+    # This is included in newest versions of pyjwt, but not the ones currently deployed,
+    # so steal their implementation over here.
+    x = jwt.utils.base64url_decode(key.get("x"))
+    y = jwt.utils.base64url_decode(key.get("y"))
+
+    try:
+        curve_obj = SECP256R1()
+        public_numbers = EllipticCurvePublicNumbers(
+            x=int.from_bytes(x, byteorder="big"),
+            y=int.from_bytes(y, byteorder="big"),
+            curve=curve_obj,
+        )
+
+        claims = jwt.decode(signed_jwt, public_numbers.public_key(), algorithms=['ES256'])
+    except jwt.exceptions.PyJWTError as e:
+        print("Exception validating jwt: {}".format(e))
+        return False
+    except Exception as ee:
+        print("Exception processing jwt: {}".format(ee))
+        return False
+
+    if claims["iat"] < time.time() - 5 * 60:
+        print("Claim expired")
+        return False
+
+    m = hashlib.sha256()
+    m.update(request.body)
+    body_hash = m.hexdigest()
+
+    if not hmac.compare_digest(body_hash, claims['request_body_sha256']):
+        print("Hash of webhook did not validate")
+        return False
+    return True
+
+
+@csrf_exempt
+def webhook(request, methodid):
+    if request.method != 'POST':
+        raise Http404()
+
+    if 'application/json' not in request.META['CONTENT_TYPE']:
+        print(request.META['CONTENT_TYPE'])
+        return HttpResponse("Invalid content type", status=400)
+
+    try:
+        j = json.loads(request.body)
+    except json.decoder.JSONDecodeError:
+        return HttpResponse("Invalid json", status=400)
+
+    # Store a copy of the webhook, for tracing
+    PlaidWebhookData(
+        source=request.META['REMOTE_ADDR'],
+        signature=request.META.get('HTTP_PLAID_VERIFICATION', ''),
+        hook_code=j.get('webhook_code', None),
+        contents=j,
+    ).save()
+
+    # Process any type of webhook we know what to do with
+
+    if j.get('webhook_type', None) == 'TRANSACTIONS' and j.get('webhook_code', None) == 'SYNC_UPDATES_AVAILABLE':
+        # Just ensure the object exists, and then throw it away, since we
+        # don't have a way to pass parameters to the job. We assume the
+        # number of plaid accounts to poll is never *that* big, and it's not
+        # like we expects several of these hooks to arrive per minute or so..
+        method = get_object_or_404(InvoicePaymentMethod, pk=methodid, classname="postgresqleu.util.payment.plaid.Plaid")
+        if not _validate_signature(request, method):
+            return HttpResponse("Invalid signature", status=400)
+
+        trigger_immediate_job_run('plaid_fetch_transactions')
+
+    return HttpResponse("OK", content_type="text/plain")