interactively prompt for passwords on login when none is provided

docs/configuration.rst

@@ -379,7 +379,7 @@ Description
     The username and password to use when attempting to log in to
     another site.
 
-    Specifying a username and password is required for
+    Specifying username and password is required for
 
     * ``nijie``
 
@@ -415,6 +415,10 @@ Description
     (*) The password value for these sites should be
     the API key found in your user profile, not the actual account password.
 
+    Note: Leave the ``password`` value empty or undefined
+    to get prompted for a passeword when performing a login
+    (see `getpass() <https://docs.python.org/3/library/getpass.html#getpass.getpass>`__).
+
 
 extractor.*.netrc
 -----------------

gallery_dl/extractor/common.py

@@ -233,7 +233,7 @@ class Extractor():
         password = None
 
         if username:
-            password = self.config("password")
+            password = self.config("password") or util.LazyPrompt()
         elif self.config("netrc", False):
             try:
                 info = netrc.netrc().authenticators(self.category)

gallery_dl/util.py

@@ -14,6 +14,7 @@ import sys
 import json
 import time
 import random
+import getpass
 import hashlib
 import sqlite3
 import binascii
@@ -487,6 +488,13 @@ CODES = {
 }
 
 
+class LazyPrompt():
+    __slots__ = ()
+
+    def __str__(self):
+        return getpass.getpass()
+
+
 class CustomNone():
     """None-style type that supports more operations than regular None"""
     __slots__ = ()