installutils: remove hardcoded subject DN assumption

`installutils.load_external_cert` assumes that the IPA CA subject
DN is `CN=Certificate Authority, {subject_base}`.  In preparation
for full customisability of IPA CA subject DN, push this assumption
out of this function to call sites (which will be updated in a
subsequent commit).

Part of: https://fedorahosted.org/freeipa/ticket/2614

Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipaserver/install/ca.py

@@ -109,7 +109,9 @@ def install_check(standalone, replica_config, options):
                   "--external-ca.")
 
         external_cert_file, external_ca_file = installutils.load_external_cert(
-            options.external_cert_files, options.subject)
+            options.external_cert_files,
+            DN(('CN', 'Certificate Authority'), options.subject)
+        )
     elif options.external_ca:
         if cainstance.is_step_one_done():
             raise ScriptError(

ipaserver/install/installutils.py

@@ -1095,7 +1095,8 @@ def check_entropy():
     except ValueError as e:
         root_logger.debug("Invalid value in %s %s", paths.ENTROPY_AVAIL, e)
 
-def load_external_cert(files, subject_base):
+
+def load_external_cert(files, ca_subject):
     """
     Load and verify external CA certificate chain from multiple files.
 
@@ -1103,7 +1104,7 @@ def load_external_cert(files, subject_base):
     chain formats.
 
     :param files: Names of files to import
-    :param subject_base: Subject name base for IPA certificates
+    :param ca_subject: IPA CA subject DN
     :returns: Temporary file with the IPA CA certificate and temporary file
         with the external CA certificate chain
     """
@@ -1117,7 +1118,7 @@ def load_external_cert(files, subject_base):
         except RuntimeError as e:
             raise ScriptError(str(e))
 
-        ca_subject = DN(('CN', 'Certificate Authority'), subject_base)
+        ca_subject = DN(ca_subject)
         ca_nickname = None
         cache = {}
         for nickname, _trust_flags in nssdb.list_certs():

ipaserver/install/ipa_cacert_manage.py

@@ -192,8 +192,6 @@ class CACertManage(admintool.AdminTool):
 
         options = self.options
         conn = api.Backend.ldap2
-        cert_file, ca_file = installutils.load_external_cert(
-            options.external_cert_files, x509.subject_base())
 
         old_cert_obj = x509.load_certificate(old_cert_der, x509.DER)
         old_der_subject = x509.get_der_subject(old_cert_der, x509.DER)
@@ -202,6 +200,11 @@ class CACertManage(admintool.AdminTool):
             serialization.PublicFormat.SubjectPublicKeyInfo
         )
 
+        cert_file, ca_file = installutils.load_external_cert(
+            options.external_cert_files,
+            DN(('CN', 'Certificate Authority'), x509.subject_base())
+        )
+
         with open(cert_file.name) as f:
             new_cert_data = f.read()
         new_cert_der = x509.normalize_certificate(new_cert_data)