ca: Intercept CSR parsing errors and convert into a custom exception

So that wsgi layer can convert it into a 4xx error, and it stops being a
5xx error + traceback.
Add a test.

caucase/ca.py

@@ -31,7 +31,10 @@ from cryptography.hazmat.primitives.asymmetric.padding import OAEP, MGF1
 from cryptography.hazmat.primitives import padding
 from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
 from . import utils
-from .exceptions import CertificateVerificationError
+from .exceptions import (
+  CertificateVerificationError,
+  NotACertificateSigningRequest,
+)
 
 __all__ = ('CertificateAuthority', )
 
@@ -289,7 +292,10 @@ class CertificateAuthority(object):
     csr_pem (str)
       PEM-encoded certificate signing request.
     """
+    try:
       csr = utils.load_certificate_request(csr_pem)
+    except ValueError:
+      raise NotACertificateSigningRequest
     # Note: requested_amount is None when a known CSR is re-submitted
     csr_id, requested_amount = self._storage.appendCertificateSigningRequest(
       csr_pem=csr_pem,

caucase/exceptions.py

@@ -38,3 +38,7 @@ class Found(CertificateAuthorityException):
 class CertificateVerificationError(CertificateAuthorityException):
   """Certificate is not valid, it was not signed by CA"""
   pass
+
+class NotACertificateSigningRequest(CertificateAuthorityException):
+  """Provided value is not a certificate signing request"""
+  pass

caucase/test.py

@@ -40,7 +40,7 @@ import unittest
 from cryptography import x509
 from cryptography.hazmat.backends import default_backend
 from caucase import cli
-from caucase.client import CaucaseError
+from caucase.client import CaucaseError, CaucaseClient
 from caucase import http
 from caucase import utils
 from caucase import exceptions
@@ -714,6 +714,20 @@ class CaucaseTest(unittest.TestCase):
       csr_id + ' not found - either csr id has a typo or CSR was rejected'
     ], out)
 
+  def testBadCSR(self):
+    """
+    Submitting an invalid CSR.
+
+    Requires bypassing cli, as it does its own checks.
+    """
+    client = CaucaseClient(self._caucase_url + '/cas')
+    try:
+      client.putCSR('Not actually a CSR')
+    except CaucaseError, e:
+      self.assertEqual(e.args[0], 400, e)
+    else:
+      raise AssertionError('Did not raise CaucaseError(400, ...)')
+
   def testUpdateUser(self):
     """
     Verify that CAU certificate and revocation list are created when the

caucase/wsgi.py

@@ -285,7 +285,10 @@ class Application(object):
     """
     if subpath:
       raise NotFound
+    try:
       csr_id = context.appendCertificateSigningRequest(self._read(environ))
+    except exceptions.NotACertificateSigningRequest:
+      raise BadRequest('Not a valid certificate signing request')
     return (
       STATUS_CREATED,
       [