server: add --ticket CLI option

Add a -t/--ticket option to the ovirt-imageio
server CLI, so that it can optionally load a
ticket directly as the server starts.

$ ovirt-imageio -c config -t path/to/ticket.json
INFO    (MainThread) [server] Starting (hostname=fedora pid=3113040, version=2.4.7)
DEBUG   (MainThread) [services] Creating remote.service on port 54322
...
INFO    (MainThread) [server] Initial ticket: examples/file.json
...
INFO    (MainThread) [server] Ready for requests

Signed-off-by: Albert Esteve <aesteve@redhat.com>

ovirt_imageio/_internal/server.py

@@ -23,6 +23,7 @@
 
 from . import auth
 from . import config
+from . import errors
 from . import services
 from . import version
 
@@ -44,7 +45,7 @@ def main():
         log.info("Starting (hostname=%s pid=%s, version=%s)",
                  socket.gethostname(), os.getpid(), version.string)
 
-        server = Server(cfg)
+        server = Server(cfg, ticket=args.ticket)
         signal.signal(signal.SIGINT, server.terminate)
         signal.signal(signal.SIGTERM, server.terminate)
 
@@ -75,6 +76,9 @@ def parse_args():
         help="print actual configuration in json format and exit. This is "
              "useful for debugging configuration issues, or reading imageio "
              "configuration by other programs.")
+    parser.add_argument(
+        "-t", "--ticket",
+        help="path to a ticket to load during server startup.")
     return parser.parse_args()
 
 
@@ -114,7 +118,7 @@ def configure_logger(cfg):
 
 class Server:
 
-    def __init__(self, config):
+    def __init__(self, config, ticket=None):
         self.config = config
         self.running = False
         self.auth = auth.Authorizer(config)
@@ -127,6 +131,9 @@ def __init__(self, config):
         if os.geteuid() == 0 and self.config.daemon.drop_privileges:
             self._drop_privileges()
 
+        if ticket:
+            self._add_ticket(ticket)
+
     def start(self):
         assert not self.running
         self.running = True
@@ -177,3 +184,17 @@ def _drop_privileges(self):
         os.initgroups(self.config.daemon.user_name, gid)
         os.setgid(gid)
         os.setuid(uid)
+
+    def _add_ticket(self, ticket):
+        log.info("Initial ticket: %s", ticket)
+        self.auth.add(self._read_ticket(ticket))
+
+    def _read_ticket(self, ticket):
+        try:
+            with open(ticket, 'r') as f:
+                return json.loads(f.read())
+        except ValueError as e:
+            raise errors.InvalidTicket(
+                f"Cannot parse ticket {ticket}: {e}") from e
+        except FileNotFoundError as e:
+            raise errors.InvalidTicket(f"Cannot read ticket: {e}") from e