UnrecognizedChallenge (fixes #855).

Overrides quick fix from #856.

acme/acme/challenges.py

@@ -25,6 +25,14 @@ class Challenge(jose.TypedJSONObjectWithFields):
     """ACME challenge."""
     TYPES = {}
 
+    @classmethod
+    def from_json(cls, jobj):
+        try:
+            return super(Challenge, cls).from_json(jobj)
+        except jose.UnrecognizedTypeError as error:
+            logger.debug(error)
+            return UnrecognizedChallenge.from_json(jobj)
+
 
 class ContinuityChallenge(Challenge):  # pylint: disable=abstract-method
     """Client validation challenges."""
@@ -34,11 +42,6 @@ class DVChallenge(Challenge):  # pylint: disable=abstract-method
     """Domain validation challenges."""
 
 
-class UnrecognizedChallenge(Challenge):
-    """Unrecognized challenge."""
-    typ = "unknown"
-
-
 class ChallengeResponse(jose.TypedJSONObjectWithFields):
     # _fields_to_partial_json | pylint: disable=abstract-method
     """ACME challenge response."""
@@ -47,6 +50,30 @@ class ChallengeResponse(jose.TypedJSONObjectWithFields):
     resource = fields.Resource(resource_type)
 
 
+class UnrecognizedChallenge(Challenge):
+    """Unrecognized challenge.
+
+    ACME specification defines a generic framework for challenges and
+    defines some standard challenges that are implemented in this
+    module. However, other implementations (including peers) might
+    define additional challenge types, which should be ignored if
+    unrecognized.
+
+    :ivar jobj: Original JSON decoded object.
+
+    """
+
+    def __init__(self, jobj):
+        object.__setattr__(self, "jobj", jobj)
+
+    def to_partial_json(self):
+        return self.jobj
+
+    @classmethod
+    def from_json(cls, jobj):
+        return cls(jobj)
+
+
 @Challenge.register
 class SimpleHTTP(DVChallenge):
     """ACME "simpleHttp" challenge.

acme/acme/messages.py

@@ -373,19 +373,7 @@ class Authorization(ResourceBody):
 
     @challenges.decoder
     def challenges(value):  # pylint: disable=missing-docstring,no-self-argument
-        # The from_json method raises errors.UnrecognizedTypeError when a
-        # challenge of unknown type is encountered.  We want to ignore this
-        # case.  This forces us to do an explicit iteration, since list
-        # comprehensions can't handle exceptions.
-        challs = []
-        for chall in value:
-            try:
-                challs.append(ChallengeBody.from_json(chall))
-            except jose.UnrecognizedTypeError:
-                challs.append(ChallengeBody(
-                    uri="UNKNOWN", chall=challenges.UnrecognizedChallenge,
-                    status=STATUS_UNKNOWN))
-        return tuple(challs)
+        return tuple(ChallengeBody.from_json(chall) for chall in value)
 
     @property
     def resolved_combinations(self):