Add tfa authenticator

CONFIG.md

@@ -131,6 +131,12 @@ via the terminal.
 - `username`: The username. (Optional)
 - `password`: The password. (Optional)
 
+### The `tfa` authenticator
+
+This authenticator prompts the user on the console for a two-factor
+authentication token. The token is provided as password and it is not cached.
+This authenticator does not support usernames.
+
 ## Transformation rules
 
 Transformation rules are rules for renaming and excluding files and directories.

PFERD/authenticators/__init__.py

@@ -1,10 +1,11 @@
 from configparser import SectionProxy
 from typing import Callable, Dict
 
-from ..authenticator import Authenticator
+from ..authenticator import Authenticator, AuthSection
 from ..conductor import TerminalConductor
 from ..config import Config
 from .simple import SimpleAuthenticator, SimpleAuthSection
+from .tfa import TfaAuthenticator
 
 AuthConstructor = Callable[[
     str,                # Name (without the "auth:" prefix)
@@ -16,4 +17,6 @@ AuthConstructor = Callable[[
 AUTHENTICATORS: Dict[str, AuthConstructor] = {
     "simple": lambda n, s, c, t:
         SimpleAuthenticator(n, SimpleAuthSection(s), c, t),
+    "tfa": lambda n, s, c, t:
+        TfaAuthenticator(n, AuthSection(s), c, t),
 }

PFERD/authenticators/tfa.py

@@ -0,0 +1,37 @@
+from typing import Tuple
+
+from ..authenticator import Authenticator, AuthException, AuthSection
+from ..conductor import TerminalConductor
+from ..config import Config
+from ..utils import ainput
+
+
+class TfaAuthenticator(Authenticator):
+    def __init__(
+            self,
+            name: str,
+            section: AuthSection,
+            config: Config,
+            conductor: TerminalConductor,
+    ) -> None:
+        super().__init__(name, section, config, conductor)
+
+    async def username(self) -> str:
+        raise AuthException("TFA authenticator does not support usernames")
+
+    async def password(self) -> str:
+        async with self.conductor.exclusive_output():
+            code = await ainput("TFA code: ")
+            return code
+
+    async def credentials(self) -> Tuple[str, str]:
+        raise AuthException("TFA authenticator does not support usernames")
+
+    def invalidate_username(self) -> None:
+        raise AuthException("TFA authenticator does not support usernames")
+
+    def invalidate_password(self) -> None:
+        pass
+
+    def invalidate_credentials(self) -> None:
+        pass