add /api/me to get identity and permissions model

identity includes fields:

- username: str
- name: Optional[str]
- display_name: Optional[str]
- initials: Optional[str]
- avatar_url: Optional[str]
- color: Optional[str]

permissions is sibling to identity,
with the form: {"resource": ["action", ],}

where permissions are only populated _by request_,
because the server cannot know what all resource/action combinations are available.

Defines new jupyter_server.auth.IdentityProvider API for implementing authorization

- IdP.get_user(Handler) returns User dataclass
- IdP.identity_model renders dataclass to standard JSON dict model
- IdP.get_handlers returns possible custom RequestHandlers (e.g. OAuth callback)
- get user_id from cookie, even when token-authenticated,
  for stable random user ids in the default implementation, even for token-authenticated requests.

Default get_user implementation still resides in LoginHandler.get_user,
to be moved and deprecated in subsequent PR.

Ensures authorizer, identity_provider are defined
in case of custom Application, load default Authorizer/IdentityProvider if none is available in settings

For CI: Fix numpy-style docstring format

docs/source/conf.py

@@ -73,6 +73,7 @@
     "sphinx.ext.intersphinx",
     "sphinx.ext.autosummary",
     "sphinx.ext.mathjax",
+    "sphinx.ext.napoleon",
     "IPython.sphinxext.ipython_console_highlighting",
     "sphinxcontrib_github_alt",
     "sphinxcontrib.openapi",
@@ -131,7 +132,7 @@
 
 # The reST default role (used for this markup: `text`) to use for all
 # documents.
-# default_role = None
+default_role = "literal"
 
 # If true, '()' will be appended to :func: etc. cross-reference text.
 # add_function_parentheses = True
@@ -360,6 +361,7 @@
     "nbconvert": ("https://nbconvert.readthedocs.io/en/latest/", None),
     "nbformat": ("https://nbformat.readthedocs.io/en/latest/", None),
     "jupyter": ("https://jupyter.readthedocs.io/en/latest/", None),
+    "tornado": ("https://www.tornadoweb.org/en/stable/", None),
 }
 
 spelling_lang = "en_US"

docs/source/operators/security.rst

@@ -77,17 +77,129 @@ but this is **NOT RECOMMENDED**, unless authentication or access restrictions ar
     c.ServerApp.token = ''
     c.ServerApp.password = ''
 
-Authorization
--------------
+
+Authentication and Authorization
+--------------------------------
 
 .. versionadded:: 2.0
 
+There are two steps to deciding whether to allow a given request to be happen.
+
+The first step is "Authentication" (identifying who is making the request).
+This is handled by the :class:`.IdentityProvider`.
+
+Whether a given user is allowed to take a specific action is called "Authorization",
+and is handled separately, by an :class:`.Authorizer`.
+
+These two classes may work together,
+as the information returned by the IdentityProvider is given to the Authorizer when it makes its decisions.
+
+Authentication always takes precedence because if no user is authenticated,
+no authorization checks need to be made,
+as all requests requiring _authorization_ must first complete _authentication_.
+
+Identity Providers
+******************
+
+The :class:`.IdentityProvider` class is responsible for the "authorization" step,
+identifying the user making the request,
+and constructing information about them.
+
+It principally implements two methods.
+
+.. autoclass:: jupyter_server.auth.IdentityProvider
+
+  .. automethod:: get_user
+  .. automethod:: identity_model
+
+The first is :meth:`.IdentityProvider.get_user`.
+This method is given a RequestHandler, and is responsible for deciding whether there is an authenticated user making the request.
+If the request is authenticated, it should return a :class:`.jupyter_server.auth.User` object representing the authenticated user.
+It should return None if the request is not authenticated.
+
+The default implementation accepts token or password authentication.
+
+This User object will be available as `self.current_user` in any request handler.
+Request methods decorated with tornado's `@web.authenticated` decorator
+will only be allowed if this method returns something.
+
+The User object will be a Python :py:class:`dataclasses.dataclass`, `jupyter_server.auth.User`:
+
+.. autoclass:: jupyter_server.auth.User
+
+A custom IdentityProvider _may_ return a custom subclass.
+
+
+The next method an identity provider has is :meth:`~.IdentityProvider.identity_model`.
+`identity_model(user)` is responsible for transforming the user object returned from `.get_user()`
+into a standard identity model dictionary,
+for use in the `/api/me` endpoint.
+
+If your user object is a simple username string or a dict with a `username` field,
+you may not need to implement this method, as the default implementation will suffice.
+
+Any required fields missing from the dict returned by this method will be filled-out with defaults.
+Only `username` is strictly required, if that is all the information the identity provider has available.
+
+Missing will be derived according to:
+
+- if `name` is missing, use `username`
+- if `display_name` is missing, use `name`
+
+Other required fields will be filled with `None`.
+
+
+Identity Model
+^^^^^^^^^^^^^^
+
+The identity model is the model accessed at `/api/me`,
+and describes the currently authenticated user.
+
+It has the following fields:
+
+username
+  (string)
+  Unique string identifying the user.
+  Must be non-empty.
+name
+  (string)
+  For-humans name of the user.
+  May be the same as `username` in systems where only usernames are available.
+display_name
+  (string)
+  Alternate rendering of name for display, such as a nickname.
+  Often the same as `name`.
+initials
+  (string or null)
+  Short string of initials.
+  Initials should not be derived automatically due to localization issues.
+  May be `null` if unavailable.
+avatar_url
+  (string or null)
+  URL of an avatar image to be used for the user.
+  May be `null` if unavailable.
+color
+  (string or null)
+  A CSS color string to use as a preferred color,
+  such as for collaboration cursors.
+  May be `null` if unavailable.
+
+Authorization
+*************
+
+Authorization is the second step in allowing an action,
+after a user has been _authenticated_ by the IdentityProvider.
+
 Authorization in Jupyter Server serves to provide finer grained control of access to its
 API resources. With authentication, requests are accepted if the current user is known by
 the server. Thus it can restrain access to specific users, but there is no way to give allowed
 users more or less permissions. Jupyter Server provides a thin and extensible authorization layer
 which checks if the current user is authorized to make a specific request.
 
+.. autoclass:: jupyter_server.auth.Authorizer
+
+  .. automethod:: is_authorized
+
 This is done by calling a ``is_authorized(handler, user, action, resource)`` method before each
 request handler. Each request is labeled as either a "read", "write", or "execute" ``action``:
 
@@ -233,6 +345,7 @@ The ``is_authorized()`` method will automatically be called whenever a handler i
 ``@authorized`` (from ``jupyter_server.auth``), similarly to the
 ``@authenticated`` decorator for authorization (from ``tornado.web``).
 
+
 Security in notebook documents
 ==============================
 

jupyter_server/auth/__init__.py

@@ -1,3 +1,4 @@
 from .authorizer import *  # noqa
 from .decorator import authorized  # noqa
+from .identity import *  # noqa
 from .security import passwd  # noqa

jupyter_server/auth/authorizer.py

@@ -11,6 +11,8 @@
 
 from jupyter_server.base.handlers import JupyterHandler
 
+from .identity import User
+
 
 class Authorizer(LoggingConfigurable):
     """Base class for authorizing access to resources
@@ -32,23 +34,28 @@ class Authorizer(LoggingConfigurable):
     .. versionadded:: 2.0
     """
 
-    def is_authorized(self, handler: JupyterHandler, user: str, action: str, resource: str) -> bool:
+    def is_authorized(
+        self, handler: JupyterHandler, user: User, action: str, resource: str
+    ) -> bool:
         """A method to determine if `user` is authorized to perform `action`
         (read, write, or execute) on the `resource` type.
 
         Parameters
         ----------
-        user : usually a dict or string
-            A truthy model representing the authenticated user.
-            A username string by default,
-            but usually a dict when integrating with an auth provider.
+        user : jupyter_server.auth.User
+            An object representing the authenticated user,
+            as returned by :meth:`.IdentityProvider.get_user`.
+
         action : str
             the category of action for the current request: read, write, or execute.
 
         resource : str
             the type of resource (i.e. contents, kernels, files, etc.) the user is requesting.
 
-        Returns True if user authorized to make request; otherwise, returns False.
+        Returns
+        -------
+        bool
+            True if user authorized to make request; False, otherwise
         """
         raise NotImplementedError()
 
@@ -61,7 +68,9 @@ class AllowAllAuthorizer(Authorizer):
     .. versionadded:: 2.0
     """
 
-    def is_authorized(self, handler: JupyterHandler, user: str, action: str, resource: str) -> bool:
+    def is_authorized(
+        self, handler: JupyterHandler, user: User, action: str, resource: str
+    ) -> bool:
         """This method always returns True.
 
         All authenticated users are allowed to do anything in the Jupyter Server.

jupyter_server/auth/decorator.py

@@ -8,7 +8,7 @@
 from tornado.log import app_log
 from tornado.web import HTTPError
 
-from .utils import HTTP_METHOD_TO_AUTH_ACTION, warn_disabled_authorization
+from .utils import HTTP_METHOD_TO_AUTH_ACTION
 
 
 def authorized(
@@ -57,18 +57,13 @@ def inner(self, *args, **kwargs):
             if not user:
                 app_log.warning("Attempting to authorize request without authentication!")
                 raise HTTPError(status_code=403, log_message=message)
-
-            # Handle the case where an authorizer wasn't attached to the handler.
-            if not self.authorizer:
-                warn_disabled_authorization()
-                return method(self, *args, **kwargs)
-
-            # Only return the method if the action is authorized.
+            # If the user is allowed to do this action,
+            # call the method.
             if self.authorizer.is_authorized(self, user, action, resource):
                 return method(self, *args, **kwargs)
-
-            # Raise an exception if the method wasn't returned (i.e. not authorized)
-            raise HTTPError(status_code=403, log_message=message)
+            # else raise an exception.
+            else:
+                raise HTTPError(status_code=403, log_message=message)
 
         return inner
 

jupyter_server/auth/identity.py

@@ -0,0 +1,139 @@
+"""Identity Provider interface
+
+This defines the _authentication_ layer of Jupyter Server,
+to be used in combination with Authorizer for _authorization_.
+
+.. versionadded:: 2.0
+"""
+from dataclasses import asdict, dataclass
+from typing import Any, Optional
+
+from tornado.web import RequestHandler
+from traitlets.config import LoggingConfigurable
+
+# from dataclasses import field
+
+
+@dataclass
+class User:
+    """Object representing a User
+
+    This or a subclass should be returned from IdentityProvider.get_user
+    """
+
+    username: str  # the only truly required field
+
+    # these fields are filled from username if not specified
+    # name is the 'real' name of the user
+    name: str = ""
+    # display_name is a shorter name for us in UI,
+    # if different from name. e.g. a nickname
+    display_name: str = ""
+
+    # these fields are left as None if undefined
+    initials: Optional[str] = None
+    avatar_url: Optional[str] = None
+    color: Optional[str] = None
+
+    # TODO: extension fields?
+    # ext: Dict[str, Dict[str, Any]] = field(default_factory=dict)
+
+    def __post_init__(self):
+        self.fill_defaults()
+
+    def fill_defaults(self):
+        """Fill out default fields in the identity model
+
+        - Ensures all values are defined
+        - Fills out derivative values for name fields fields
+        - Fills out null values for optional fields
+        """
+
+        # username is the only truly required field
+        if not self.username:
+            raise ValueError(f"user.username must not be empty: {self}")
+
+        # derive name fields from username -> name -> display name
+        if not self.name:
+            self.name = self.username
+        if not self.display_name:
+            self.display_name = self.name
+
+    def to_dict(self):
+        pass
+
+
+def _backward_compat_user(got_user: Any) -> User:
+    """Backward-compatibility for LoginHandler.get_user
+
+    Prior to 2.0, LoginHandler.get_user could return anything truthy.
+
+    Typically, this was either a simple string username,
+    or a simple dict.
+
+    Make some effort to allow common patterns to keep working.
+    """
+    if isinstance(got_user, str):
+        return User(username=got_user)
+    elif isinstance(got_user, dict):
+        kwargs = {}
+        if "username" not in got_user:
+            if "name" in got_user:
+                kwargs["username"] = got_user["name"]
+        for field in User.__dataclass_fields__:
+            if field in got_user:
+                kwargs[field] = got_user[field]
+        try:
+            return User(**kwargs)
+        except TypeError:
+            raise ValueError(f"Unrecognized user: {got_user}")
+    else:
+        raise ValueError(f"Unrecognized user: {got_user}")
+
+
+class IdentityProvider(LoggingConfigurable):
+    """
+    Interface for providing identity
+
+    Two principle methods:
+
+    - :meth:`~.IdentityProvider.get_user` returns a :class:`~.User` object
+      for successful authentication, or None for no-identity-found.
+    - :meth:`~.IdentityProvider.identity_model` turns a :class:`~.User` into a JSONable dict.
+      The default is to use :py:meth:`dataclasses.asdict`,
+      and usually shouldn't need override.
+
+    .. versionadded:: 2.0
+    """
+
+    def get_user(self, handler: RequestHandler) -> User:
+        """Get the authenticated user for a request
+
+        Must return a :class:`.jupyter_server.auth.User`,
+        though it may be a subclass.
+
+        Return None if the request is not authenticated.
+        """
+
+        if handler.login_handler is None:
+            return User("anonymous")
+
+        # The default: call LoginHandler.get_user for backward-compatibility
+        # TODO: move default implementation to this class,
+        # deprecate `LoginHandler.get_user`
+        user = handler.login_handler.get_user(handler)
+        if user and not isinstance(user, User):
+            return _backward_compat_user(user)
+        return user
+
+    def identity_model(self, user: User) -> dict:
+        """Return a User as an Identity model"""
+        # TODO: validate?
+        return asdict(user)
+
+    def get_handlers(self) -> list:
+        """Return list of additional handlers for this identity provider
+
+        For example, an OAuth callback handler.
+        """
+        return []