Allow piping the password to login_cli

This is useful for testing where entering a password manually is not
possible.

changelog.yaml

@@ -4,6 +4,7 @@
     - "Add `--scheduled-at` option to `toot post`, allows scheduling toots"
     - "Add `--description` option to `toot post`, for adding descriptions to media attachments (thanks @ansuz)"
     - "Disable paging timeline when output is piped (thanks @stacyharper)"
+    - "Allow piping the password to login_cli for testing purposes (thanks @NinjaTrappeur)"
 
 0.27.0:
   date: 2020-06-15

toot/auth.py

@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 
+import sys
 import webbrowser
 
 from builtins import input
@@ -66,7 +67,13 @@ def login_interactive(app, email=None):
     while not email:
         email = input('Email: ')
 
-    password = getpass('Password: ')
+    # Accept password piped from stdin, useful for testing purposes but not
+    # documented so people won't get ideas. Otherwise prompt for password.
+    if sys.stdin.isatty():
+        password = getpass('Password: ')
+    else:
+        password = sys.stdin.read().strip()
+        print_out("Password: <green>read from stdin</green>")
 
     try:
         print_out("Authenticating...")