How to use the tuf.repository_tool.import_rsa_publickey_from_file function in tuf

# Store and return the cryptography keys of the top-level roles, including 1
  # delegated role.
  role_keys = {}

  root_key_file = os.path.join(keystore_directory, 'root_key')
  targets_key_file = os.path.join(keystore_directory, 'targets_key')
  snapshot_key_file = os.path.join(keystore_directory, 'snapshot_key')
  timestamp_key_file = os.path.join(keystore_directory, 'timestamp_key')
  delegation_key_file = os.path.join(keystore_directory, 'delegation_key')

  role_keys = {'root': {}, 'targets': {}, 'snapshot': {}, 'timestamp': {},
               'role1': {}}

  # Import the top-level and delegated role public keys.
  role_keys['root']['public'] = \
    repo_tool.import_rsa_publickey_from_file(root_key_file+'.pub')
  role_keys['targets']['public'] = \
    repo_tool.import_ed25519_publickey_from_file(targets_key_file + '.pub')
  role_keys['snapshot']['public'] = \
    repo_tool.import_ed25519_publickey_from_file(snapshot_key_file + '.pub')
  role_keys['timestamp']['public'] = \
      repo_tool.import_ed25519_publickey_from_file(timestamp_key_file + '.pub')
  role_keys['role1']['public'] = \
      repo_tool.import_ed25519_publickey_from_file(delegation_key_file + '.pub')

  # Import the private keys of the top-level and delegated roles.
  role_keys['root']['private'] = \
    repo_tool.import_rsa_privatekey_from_file(root_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)
  role_keys['targets']['private'] = \
    repo_tool.import_ed25519_privatekey_from_file(targets_key_file,
                                              EXPECTED_KEYFILE_PASSWORD)

# (1) Load the public and private keys of the top-level roles, and one
    # delegated role.
    keystore_directory = os.path.join('repository_data', 'keystore')

    # Load the public keys.
    root_pubkey_path = os.path.join(keystore_directory, 'root_key.pub')
    targets_pubkey_path = os.path.join(keystore_directory, 'targets_key.pub')
    snapshot_pubkey_path = os.path.join(keystore_directory, 'snapshot_key.pub')
    timestamp_pubkey_path = os.path.join(keystore_directory, 'timestamp_key.pub')
    role1_pubkey_path = os.path.join(keystore_directory, 'delegation_key.pub')

    root_pubkey = repo_tool.import_rsa_publickey_from_file(root_pubkey_path)
    targets_pubkey = repo_tool.import_ed25519_publickey_from_file(targets_pubkey_path)
    snapshot_pubkey = \
      repo_tool.import_ed25519_publickey_from_file(snapshot_pubkey_path)
    timestamp_pubkey = \
      repo_tool.import_ed25519_publickey_from_file(timestamp_pubkey_path)
    role1_pubkey = repo_tool.import_ed25519_publickey_from_file(role1_pubkey_path)

    # Load the private keys.
    root_privkey_path = os.path.join(keystore_directory, 'root_key')
    targets_privkey_path = os.path.join(keystore_directory, 'targets_key')
    snapshot_privkey_path = os.path.join(keystore_directory, 'snapshot_key')
    timestamp_privkey_path = os.path.join(keystore_directory, 'timestamp_key')
    role1_privkey_path = os.path.join(keystore_directory, 'delegation_key')

    root_privkey = \
      repo_tool.import_rsa_privatekey_from_file(root_privkey_path, 'password')

def test_get_delegated_rolenames(self):
    # Test normal case.
    # Perform two delegations so that get_delegated_rolenames() has roles to 
    # return.
    keystore_directory = os.path.join('repository_data', 'keystore')
    public_keypath = os.path.join(keystore_directory, 'root_key.pub')
    public_key = repo_tool.import_rsa_publickey_from_file(public_keypath)
    target1_filepath = os.path.join(self.targets_directory, 'file1.txt')
    target2_filepath = os.path.join(self.targets_directory, 'file2.txt')

    # Set needed arguments by delegate().
    public_keys = [public_key]
    threshold = 1

    self.targets_object.delegate('tuf', public_keys, [target1_filepath],
                                 threshold, restricted_paths=None,
                                 path_hash_prefixes=None)
    self.targets_object.delegate('warehouse', public_keys, [target2_filepath],
                                 threshold, restricted_paths=None,
                                 path_hash_prefixes=None)

    # Test that get_delegated_rolenames returns the expected delegations.
    expected_delegated_rolenames = ['targets/tuf/', 'targets/warehouse']

public_snap_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'snap.pub')
  public_targets_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'targets.pub')
  private_time_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'time', password='pw')
  private_snap_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'snap', password='pw')
  if not online_only:
    private_root_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'root', password='pw')
    private_targets_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'targets', password='pw')

  # Import delegated keys.
  public_images_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'images.pub')
  public_director_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'director.pub')
  public_brakes_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'brakes.pub')
  public_acme_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'acme.pub')
  public_cell_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'cell.pub')
  private_director_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'director', password='pw')
  if not online_only:
    private_images_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'images', password='pw')
    private_brakes_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'brakes', password='pw')

public_targets_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'targets.pub')
  private_time_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'time', password='pw')
  private_snap_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'snap', password='pw')
  if not online_only:
    private_root_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'root', password='pw')
    private_targets_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'targets', password='pw')

  # Import delegated keys.
  public_images_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'images.pub')
  public_director_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'director.pub')
  public_brakes_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'brakes.pub')
  public_acme_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'acme.pub')
  public_cell_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'cell.pub')
  private_director_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'director', password='pw')
  if not online_only:
    private_images_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'images', password='pw')
    private_brakes_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'brakes', password='pw')
    private_acme_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'acme', password='pw')

private_snap_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'snap', password='pw')
  if not online_only:
    private_root_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'root', password='pw')
    private_targets_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'targets', password='pw')

  # Import delegated keys.
  public_images_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'images.pub')
  public_director_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'director.pub')
  public_brakes_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'brakes.pub')
  public_acme_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'acme.pub')
  public_cell_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'cell.pub')
  private_director_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'director', password='pw')
  if not online_only:
    private_images_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'images', password='pw')
    private_brakes_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'brakes', password='pw')
    private_acme_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'acme', password='pw')
    private_cell_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'cell', password='pw')

global private_root_key
  global private_time_key
  global private_snap_key
  global private_targets_key
  global private_images_key
  global private_director_key
  global private_brakes_key
  global private_acme_key
  global private_cell_key

  # Import public and private keys from the generated files.
  public_root_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'root.pub')
  public_time_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'time.pub')
  public_snap_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'snap.pub')
  public_targets_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'targets.pub')
  private_time_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'time', password='pw')
  private_snap_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'snap', password='pw')
  if not online_only:
    private_root_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'root', password='pw')
    private_targets_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'targets', password='pw')

  # Import delegated keys.
  public_images_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'images.pub')

global public_director_key
  global public_brakes_key
  global public_acme_key
  global public_cell_key
  global private_root_key
  global private_time_key
  global private_snap_key
  global private_targets_key
  global private_images_key
  global private_director_key
  global private_brakes_key
  global private_acme_key
  global private_cell_key

  # Import public and private keys from the generated files.
  public_root_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'root.pub')
  public_time_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'time.pub')
  public_snap_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'snap.pub')
  public_targets_key = repotool.import_rsa_publickey_from_file(KEYS_DIR +
      'targets.pub')
  private_time_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'time', password='pw')
  private_snap_key = repotool.import_rsa_privatekey_from_file(KEYS_DIR +
      'snap', password='pw')
  if not online_only:
    private_root_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'root', password='pw')
    private_targets_key = repotool.import_rsa_privatekey_from_file(
        KEYS_OFFLINE_DIR + 'targets', password='pw')