Service: common method for service keytab requests

Since creation of service principals and keytab retrieval are common
operations, Service class should provide means to add service entry to LDAP,
retrieve its keytab to designated destination and change the owner to service
user.

https://fedorahosted.org/freeipa/ticket/6405

Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>

ipaserver/install/service.py

@@ -19,6 +19,7 @@
 
 import sys
 import os
+import pwd
 import socket
 import datetime
 import traceback
@@ -165,6 +166,7 @@ class Service(object):
         self.dercert = None
         self.api = api
         self.service_user = service_user
+        self.dm_password = None  # silence pylint
 
     @property
     def admin_conn(self):
@@ -534,6 +536,58 @@ class Service(object):
         else:
             root_logger.debug("service %s container sucessfully removed", name)
 
+    def _add_service_principal(self):
+        try:
+            self.api.Command.service_add(self.principal, force=True)
+        except errors.DuplicateEntry:
+            pass
+
+    def _run_getkeytab(self):
+        """
+        backup and remove old service keytab (if present) and fetch a new one
+        using ipa-getkeytab. This assumes that the service principal is already
+        created in LDAP. By default GSSAPI authentication is used unless:
+            * LDAPI socket is used and effective process UID is 0, then
+              autobind is used by EXTERNAL SASL mech
+            * self.dm_password is not none, then DM credentials are used to
+              fetch keytab
+        """
+        self.fstore.backup_file(self.keytab)
+        try:
+            os.unlink(self.keytab)
+        except OSError:
+            pass
+
+        ldap_uri = self.api.env.ldap_uri
+        args = [paths.IPA_GETKEYTAB,
+                '-k', self.keytab,
+                '-p', self.principal,
+                '-H', ldap_uri]
+        nolog = tuple()
+
+        if ldap_uri.startswith("ldapi://") and os.geteuid() == 0:
+            args.extend(["-Y", "EXTERNAL"])
+        elif self.dm_password is not None:
+            args.extend(
+                ['-D', 'cn=Directory Manager',
+                 '-w', self.dm_password])
+            nolog += (self.dm_password,)
+
+        ipautil.run(args, nolog=nolog)
+
+    def _request_service_keytab(self):
+        if any(attr is None for attr in (self.principal, self.keytab,
+                                         self.service_user)):
+            raise NotImplementedError(
+                "service must have defined principal "
+                "name, keytab, and username")
+
+        self._add_service_principal()
+        self._run_getkeytab()
+
+        pent = pwd.getpwnam(self.service_user)
+        os.chown(self.keytab, pent.pw_uid, pent.pw_gid)
+
 
 class SimpleServiceInstance(Service):
     def create_instance(self, gensvc_name=None, fqdn=None, ldap_suffix=None,