Add errors.FailedChallenges and update AuthHandler to use it.

letsencrypt/errors.py

@@ -14,6 +14,24 @@ class AuthorizationError(LetsEncryptClientError):
     """Authorization error."""
 
 
+class FailedChallenges(AuthorizationError):
+    """Failed challenges error.
+
+    :ivar set failed_achalls: Failed `.AnnotatedChallenge` instances.
+
+    """
+    def __init__(self, failed_achalls):
+        assert failed_achalls
+        self.failed_achalls = failed_achalls
+        super(FailedChallenges, self).__init__()
+
+    def __str__(self):
+        return "Failed authorization procedure. {0}".format(
+            ", ".join(
+                "{0} ({1}): {2}".format(achall.domain, achall.typ, achall.error)
+                for achall in self.failed_achalls if achall.error is not None))
+
+
 class LetsEncryptContAuthError(AuthorizationError):
     """Let's Encrypt Continuity Authenticator error."""