Only prompt for a password if the server asks for it

In many cases the session cookie is already available, so there
is no need to ask for a password. To make this work with the
python authentication implementation, we add a small proxy object
for the password and only ask the credential manager if the
stringify method is called.

This approach also makes it possible to offer a non-password based
authorization type if the server allows multiple authentication
methods.

osc/conf.py

@@ -764,7 +764,7 @@ def config_set_option(section, opt, val=None, delete=False, update=True, creds_m
         # change password store
         creds_mgr = _get_credentials_manager(section, cp)
         user = _extract_user_compat(cp, section, creds_mgr)
-        val = creds_mgr.get_password(section, user)
+        val = creds_mgr.get_password(section, user, defer=False)
 
     run = False
     if val:
@@ -884,6 +884,8 @@ class APIHostOptionsEntry(dict):
     def __getitem__(self, key, *args, **kwargs):
         value = super(self.__class__, self).__getitem__(key, *args, **kwargs)
         if key == 'pass' and callable(value):
+            print('Warning: use of a deprecated credentials manager API.',
+                  file=sys.stderr)
             value = value()
         return value
 
@@ -979,7 +981,7 @@ def get_config(override_conffile=None,
         user = _extract_user_compat(cp, url, creds_mgr)
         if user is None:
             raise oscerr.ConfigMissingCredentialsError('No user found in section %s' % url, conffile, url)
-        password = creds_mgr.get_password(url, user)
+        password = creds_mgr.get_password(url, user, defer=True)
         if password is None:
             raise oscerr.ConfigMissingCredentialsError('No password found in section %s' % url, conffile, url)
 

osc/credentials.py

@@ -33,6 +33,31 @@ from . import conf
 from . import oscerr
 
 
+class _LazyPassword(object):
+    def __init__(self, pwfunc):
+        self._pwfunc = pwfunc
+        self._password = None
+
+    def __str__(self):
+        if self._password is None:
+            self._password = self._pwfunc()
+            if self._password is None:
+                raise oscerr.OscIOError(None, 'Unable to retrieve password')
+        return self._password
+
+    def __len__(self):
+        return len(str(self))
+
+    def __add__(self, other):
+        return str(self) + other
+
+    def __radd__(self, other):
+        return other + str(self)
+
+    def __getattr__(self, name):
+        return getattr(str(self), name)
+
+
 class AbstractCredentialsManagerDescriptor(object):
     def name(self):
         raise NotImplementedError()
@@ -64,14 +89,15 @@ class AbstractCredentialsManager(object):
     def create(cls, cp, options):
         return cls(cp, options)
 
-    def get_password(self, url, user, defer=True):
-        # If defer is True a callable can be returned
-        # and the password is retrieved if the callable
-        # is called. Implementations are free to ignore
-        # defer parameter and can directly return the password.
-        # If defer is False the password is directly returned.
+    def _get_password(self, url, user):
         raise NotImplementedError()
 
+    def get_password(self, url, user, defer=True):
+        if defer:
+            return _LazyPassword(lambda: self._get_password(url, user))
+        else:
+            return self._get_password(url, user)
+
     def set_password(self, url, user, password):
         raise NotImplementedError()
 
@@ -162,10 +188,10 @@ class TransientCredentialsManager(AbstractCredentialsManager):
         if options is not None:
             raise RuntimeError('options must be None')
 
-    def get_password(self, url, user, defer=True):
-        if defer:
-            return self
-        return self()
+    def _get_password(self, url, user):
+        if self._password is None:
+            self._password = getpass.getpass('Password: ')
+        return self._password
 
     def set_password(self, url, user, password):
         self._password = password
@@ -174,11 +200,6 @@ class TransientCredentialsManager(AbstractCredentialsManager):
     def delete_password(self, url, user):
         self._password = None
 
-    def __call__(self):
-        if self._password is None:
-            self._password = getpass.getpass('Password: ')
-        return self._password
-
 
 class TransientDescriptor(AbstractCredentialsManagerDescriptor):
     def name(self):
@@ -214,7 +235,7 @@ class KeyringCredentialsManager(AbstractCredentialsManager):
             return None
         return super(cls, cls).create(cp, options)
 
-    def get_password(self, url, user, defer=True):
+    def _get_password(self, url, user):
         self._load_backend()
         return keyring.get_password(urlsplit(url)[1], user)
 
@@ -265,7 +286,7 @@ class GnomeKeyringCredentialsManager(AbstractCredentialsManager):
             return None
         return super(cls, cls).create(cp, options)
 
-    def get_password(self, url, user, defer=True):
+    def _get_password(self, url, user):
         gk_data = self._keyring_data(url, user)
         if gk_data is None:
             return None