Authenticate from mounted secrets and stop passing the password to seaf-cli

The password could only be given through the PASSWORD variable, so Docker
Compose and Swarm secrets were unusable and the password sat in the container
environment.

PASSWORD_FILE and TOKEN_FILE read a secret from a mounted file. Only trailing
newlines are stripped, since secret files are usually written with one and a
password that silently carries it just fails to authenticate; everything else,
including surrounding spaces, belongs to the secret. Setting both a variable
and a file for one secret is rejected rather than resolved by precedence,
because the two are meant to be the same value and quietly picking one hides
the mistake until authentication fails.

The installed seaf-cli supports token authentication and ignores the password
when a token is given, so sync now passes -T instead of -p. The account
password no longer appears in any command line. The token does, because
seaf-cli accepts credentials only as arguments, but a token can be revoked on
the server. This is documented in the README.

Both secrets are masked before a command is logged.

Tests cover newline handling, empty and missing files, conflicting sources,
and that neither secret reaches the logs. Requests are now blocked in tests:
the client retries with backoff, so a test that reached the network appeared
to hang instead of failing.

tests/test_commands.py

@@ -8,7 +8,7 @@ import pytest
 from dsc import client as client_module
 from dsc import const
 from dsc.client import SeafileClient
-from dsc.misc import hide_password, user_cmd
+from dsc.misc import hide_secrets, user_cmd
 
 # Values that would be interpreted by a shell if a command were ever joined
 # into a string and handed to ``su -c``.
@@ -34,6 +34,7 @@ def client():
         user="user@example",
         passwd="s3cret",
         app_dir="/dsc",
+        token="tok-en",
     )
 
 
@@ -71,13 +72,21 @@ def test_user_cmd_rejects_a_string():
         user_cmd("seaf-cli status")
 
 
-@pytest.mark.parametrize("password", SHELL_METACHARACTERS)
-def test_sync_passes_password_as_one_unquoted_argument(client, calls, password):
-    client.password = password
+@pytest.mark.parametrize("secret", SHELL_METACHARACTERS)
+def test_sync_passes_the_token_as_one_unquoted_argument(client, calls, secret):
+    client._SeafileClient__token = secret
     client.sync_lib("lib-id", "/dsc/seafile/Docs")
 
     argv, _ = calls[-1]
-    assert argv[argv.index("-p") + 1] == password
+    assert argv[argv.index("-T") + 1] == secret
+
+
+def test_sync_authenticates_with_the_token_not_the_password(client, calls):
+    client.sync_lib("lib-id", "/dsc/seafile/Docs")
+
+    argv, _ = calls[-1]
+    assert "-p" not in argv, "the account password must never reach argv"
+    assert client.password not in argv
 
 
 @pytest.mark.parametrize("lib_dir", [
@@ -102,23 +111,34 @@ def test_sync_command_is_a_list_of_strings(client, calls):
     assert kwargs.get("shell") is not True
 
 
-@pytest.mark.parametrize("password", SHELL_METACHARACTERS)
-def test_sync_never_logs_the_password(client, calls, caplog, password):
-    client.password = password
+@pytest.mark.parametrize("secret", SHELL_METACHARACTERS)
+def test_sync_never_logs_the_token_or_the_password(client, calls, caplog, secret):
+    client._SeafileClient__token = secret
+    client.password = secret + "-pw"
     with caplog.at_level("INFO"):
         client.sync_lib("lib-id", "/dsc/seafile/Docs")
 
-    assert password not in caplog.text
+    assert secret not in caplog.text
+    assert client.password not in caplog.text
 
 
-def test_hide_password_masks_every_occurrence():
-    masked = hide_password(["-p", "secret", "-u", "secret-user"], "secret")
+def test_hide_secrets_masks_every_occurrence():
+    masked = hide_secrets(["-p", "secret", "-u", "secret-user"], "secret")
     assert masked == ["-p", "********", "-u", "********-user"]
 
 
-def test_hide_password_does_not_mutate_the_original():
+def test_hide_secrets_masks_several_secrets():
+    masked = hide_secrets(["-p", "pw", "-T", "tok"], "pw", "tok")
+    assert masked == ["-p", "********", "-T", "********"]
+
+
+def test_hide_secrets_ignores_secrets_that_are_not_set():
+    assert hide_secrets(["-T", "tok"], None, "tok") == ["-T", "********"]
+
+
+def test_hide_secrets_does_not_mutate_the_original():
     argv = ["-p", "secret"]
-    hide_password(argv, "secret")
+    hide_secrets(argv, "secret")
     assert argv == ["-p", "secret"]