Handle missing LWCA certificate or chain

If lightweight CA key replication has not completed, requests for
the certificate or chain will return 404**.  This can occur in
normal operation, and should be a temporary condition.  Detect this
case and handle it by simply omitting the 'certificate' and/or
'certificate_out' fields in the response, and add a warning message
to the response.

Also update the client-side plugin that handles the
--certificate-out option.  Because the CLI will automatically print
the warning message, if the expected field is missing from the
response, just ignore it and continue processing.

** after the Dogtag NullPointerException gets fixed!

Part of: https://pagure.io/freeipa/issue/7964

Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>

ipaserver/plugins/ca.py

@@ -6,7 +6,7 @@ import base64
 
 import six
 
-from ipalib import api, errors, output, Bytes, DNParam, Flag, Str
+from ipalib import api, errors, messages, output, Bytes, DNParam, Flag, Str
 from ipalib.constants import IPA_CA_CN
 from ipalib.plugable import Registry
 from ipapython.dn import ATTR_NAME_BY_OID
@@ -163,28 +163,53 @@ class ca(LDAPObject):
 
 
 def set_certificate_attrs(entry, options, want_cert=True):
+    """
+    Set certificate attributes into the entry.  Depending on
+    options, this may contact Dogtag to retrieve certificate or
+    chain.  If the retrieval fails with 404 (which can occur under
+    normal operation due to lightweight CA key replication delay),
+    return a message object that should be set in the response.
+
+    """
     try:
         ca_id = entry['ipacaid'][0]
     except KeyError:
-        return
+        return None
     full = options.get('all', False)
     want_chain = options.get('chain', False)
 
     want_data = want_cert or want_chain or full
     if not want_data:
-        return
+        return None
+
+    msg = None
 
     with api.Backend.ra_lightweight_ca as ca_api:
         if want_cert or full:
-            der = ca_api.read_ca_cert(ca_id)
-            entry['certificate'] = base64.b64encode(der).decode('ascii')
+            try:
+                der = ca_api.read_ca_cert(ca_id)
+                entry['certificate'] = base64.b64encode(der).decode('ascii')
+            except errors.HTTPRequestError as e:
+                if e.status == 404:  # pylint: disable=no-member
+                    msg = messages.LightweightCACertificateNotAvailable(
+                        ca=entry['cn'][0])
+                else:
+                    raise e
 
         if want_chain or full:
-            pkcs7_der = ca_api.read_ca_chain(ca_id)
-            certs = x509.pkcs7_to_certs(pkcs7_der, x509.DER)
-            ders = [cert.public_bytes(x509.Encoding.DER) for cert in certs]
-            entry['certificate_chain'] = ders
+            try:
+                pkcs7_der = ca_api.read_ca_chain(ca_id)
+                certs = x509.pkcs7_to_certs(pkcs7_der, x509.DER)
+                ders = [cert.public_bytes(x509.Encoding.DER) for cert in certs]
+                entry['certificate_chain'] = ders
+            except errors.HTTPRequestError as e:
+                if e.status == 404:  # pylint: disable=no-member
+                    msg = messages.LightweightCACertificateNotAvailable(
+                        ca=entry['cn'][0])
+                else:
+                    raise e
 
+    return msg
 
 @register()
 class ca_find(LDAPSearch):
@@ -198,7 +223,9 @@ class ca_find(LDAPSearch):
         result = super(ca_find, self).execute(*keys, **options)
         if not options.get('pkey_only', False):
             for entry in result['result']:
-                set_certificate_attrs(entry, options, want_cert=False)
+                msg = set_certificate_attrs(entry, options, want_cert=False)
+                if msg:
+                    self.add_message(msg)
         return result
 
 
@@ -220,7 +247,9 @@ class ca_show(LDAPRetrieve):
     def execute(self, *keys, **options):
         ca_enabled_check(self.api)
         result = super(ca_show, self).execute(*keys, **options)
-        set_certificate_attrs(result['result'], options)
+        msg = set_certificate_attrs(result['result'], options)
+        if msg:
+            self.add_message(msg)
         return result
 
 
@@ -284,7 +313,9 @@ class ca_add(LDAPCreate):
         return dn
 
     def post_callback(self, ldap, dn, entry_attrs, *keys, **options):
-        set_certificate_attrs(entry_attrs, options)
+        msg = set_certificate_attrs(entry_attrs, options)
+        if msg:
+            self.add_message(msg)
         return dn