Allow CustodiaClient to be used by arbitrary principals

Currently CustodiaClient assumes that the client is the host
principal, and it is hard-coded to read the host keytab and server
keys.

For the Lightweight CAs feature, Dogtag on CA replicas will use
CustodiaClient to retrieve signing keys from the originating
replica.  Because this process runs as 'pkiuser', the host keys
cannot be used; instead, each Dogtag replica will have a service
principal to use for Custodia authentication.

Update CustodiaClient to require specifying the client keytab and
Custodia keyfile to use, and change the client argument to be a full
GSS service name (instead of hard-coding host service) to load from
the keytab.  Update call sites accordingly.

Also pass the given 'ldap_uri' argument through to IPAKEMKeys
because without it, the client tries to use LDAPI, but may not have
access.

Part of: https://fedorahosted.org/freeipa/ticket/4559

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

ipapython/secrets/client.py

@@ -41,16 +41,22 @@ class CustodiaClient(object):
 
         return iSecStore(config)
 
-    def __init__(self, client, server, realm, ldap_uri=None, auth_type=None):
-        self.client = client
-        self.creds = None
+    def __init__(
+            self, client_service, keyfile, keytab, server, realm,
+            ldap_uri=None, auth_type=None):
+        self.client_service = client_service
+        self.keytab = keytab
+
+        # Init creds immediately to make sure they are valid.  Creds
+        # can also be re-inited by _auth_header to avoid expiry.
+        #
+        self.creds = self.init_creds()
 
         self.service_name = gssapi.Name('HTTP@%s' % (server,),
                                         gssapi.NameType.hostbased_service)
         self.server = server
 
-        keyfile = os.path.join(paths.IPA_CUSTODIA_CONF_DIR, 'server.keys')
-        self.ikk = IPAKEMKeys({'server_keys': keyfile})
+        self.ikk = IPAKEMKeys({'server_keys': keyfile, 'ldap_uri': ldap_uri})
 
         self.kemcli = KEMClient(self._server_keys(server, realm),
                                 self._client_keys())
@@ -61,9 +67,9 @@ class CustodiaClient(object):
         requests.packages.urllib3.disable_warnings()
 
     def init_creds(self):
-        name = gssapi.Name('host@%s' % (self.client,),
+        name = gssapi.Name(self.client_service,
                            gssapi.NameType.hostbased_service)
-        store = {'client_keytab': paths.KRB5_KEYTAB,
+        store = {'client_keytab': self.keytab,
                  'ccache': 'MEMORY:Custodia_%s' % b64encode(os.urandom(8))}
         return gssapi.Credentials(name=name, store=store, usage='initiate')