Have --auth prompt for password if omitted.

httpie/cli.py

@@ -123,8 +123,11 @@ parser.add_argument(
 
 # ``requests.request`` keyword arguments.
 parser.add_argument(
-    '--auth', '-a', help='username:password',
-    type=cliparse.KeyValueType(cliparse.SEP_COMMON)
+    '--auth', '-a', type=cliparse.AuthCredentials(cliparse.SEP_COMMON),
+    help=_('''
+        username:password.
+        If the password is omitted, HTTPie will prompt for it.
+    '''),
 )
 
 parser.add_argument(

httpie/cliparse.py

@@ -10,6 +10,7 @@ import argparse
 import mimetypes
 
 from collections import namedtuple
+from getpass import getpass
 
 try:
     from collections import OrderedDict
@@ -204,6 +205,20 @@ class KeyValueType(object):
         return KeyValue(key=key, value=value, sep=sep, orig=string)
 
 
+class AuthCredentials(KeyValueType):
+    def __call__(self, string):
+        try:
+            return super(AuthCredentials, self).__call__(string)
+        except argparse.ArgumentTypeError:
+            try:
+                password = getpass("Password for user '%s': " % string)
+            except (EOFError, KeyboardInterrupt):
+                sys.stderr.write('\n')
+                sys.exit(0)
+            return KeyValue(key=string, value=password, sep=SEP_COMMON,
+                            orig=string)
+
+
 def parse_items(items, data=None, headers=None, files=None):
     """Parse `KeyValueType` `items` into `data`, `headers` and `files`."""
     if headers is None: