cloud-init: change rand_user_password to secrets

The "secrets" submodule is more secure than "random". See [1].

[1] https://docs.python.org/3/library/secrets.html

subiquity/cloudinit.py

@@ -3,8 +3,8 @@
 import asyncio
 import json
 import logging
-import random
 import re
+import secrets
 from collections.abc import Awaitable, Sequence
 from string import ascii_letters, digits
 from subprocess import CompletedProcess
@@ -162,8 +162,8 @@ async def validate_cloud_init_schema() -> None:
     return None
 
 
-def rand_str(strlen: int = 32, select_from: Optional[Sequence] = None) -> str:
-    r: random.SystemRandom = random.SystemRandom()
+def rand_password(strlen: int = 32, select_from: Optional[Sequence] = None) -> str:
+    r: secrets.SystemRandom = secrets.SystemRandom()
     if not select_from:
         select_from: str = ascii_letters + digits
     return "".join([r.choice(select_from) for _x in range(strlen)])
@@ -172,4 +172,4 @@ def rand_str(strlen: int = 32, select_from: Optional[Sequence] = None) -> str:
 # Generate random user passwords the same way cloud-init does
 # https://github.com/canonical/cloud-init/blob/6e4153b346bc0d3f3422c01a3f93ecfb28269da2/cloudinit/config/cc_set_passwords.py#L249  # noqa: E501
 def rand_user_password(pwlen: int = 20) -> str:
-    return rand_str(strlen=pwlen, select_from=CLOUD_INIT_PW_SET)
+    return rand_password(strlen=pwlen, select_from=CLOUD_INIT_PW_SET)

subiquity/tests/test_cloudinit.py

@@ -24,7 +24,7 @@
     cloud_init_status_wait,
     cloud_init_version,
     get_schema_failure_keys,
-    rand_str,
+    rand_password,
     rand_user_password,
     read_json_extended_status,
     read_legacy_status,
@@ -238,13 +238,13 @@ def test_passwd_constraints(self):
 
     def test_rand_string_generation(self):
         # random string is 32 characters by default
-        password = rand_str()
+        password = rand_password()
         self.assertEqual(len(password), 32)
 
         # password is requested length
-        password = rand_str(strlen=20)
+        password = rand_password(strlen=20)
         self.assertEqual(len(password), 20)
 
         # password characters sampled from provided set
         choices = ["a"]
-        self.assertEqual("a" * 32, rand_str(select_from=choices))
+        self.assertEqual("a" * 32, rand_password(select_from=choices))