AuthorManager: New getAuthorId hook

CHANGELOG.md

@@ -40,6 +40,7 @@
 
 * New `expressPreSession` server-side hook.
 * New `padDefaultContent` server-side hook.
+* New `getAuthorId` server-side hook.
 * New APIs for processing attributes: `ep_etherpad-lite/static/js/attributes`
   (low-level API) and `ep_etherpad-lite/static/js/AttributeMap` (high-level
   API).
@@ -79,6 +80,8 @@
   * `appendATextToAssembler()`: Deprecated in favor of the new `opsFromAText()`
     generator function.
   * `newOp()`: Deprecated in favor of the new `Op` class.
+* The `AuthorManager.getAuthor4Token()` function is deprecated; use the new
+  `AuthorManager.getAuthorId()` function instead.
 
 # 1.8.17
 

doc/api/hooks_server-side.md

@@ -207,6 +207,62 @@ Things in context:
 This hook gets called when the access to the concrete pad is being checked.
 Return `false` to deny access.
 
+## `getAuthorId`
+
+Called from `src/node/db/AuthorManager.js`
+
+Called when looking up (or creating) the author ID for a user, except for author
+IDs obtained via the HTTP API. Registered hook functions are called until one
+returns a non-`undefined` value. If a truthy value is returned by a hook
+function, it is used as the user's author ID. Otherwise, the value of the
+`dbKey` context property is used to look up the author ID. If there is no such
+author ID at that key, a new author ID is generated and associated with that
+key.
+
+Context properties:
+
+* `dbKey`: Database key to use when looking up the user's author ID if no hook
+  function returns an author ID. This is initialized to the user-supplied token
+  value (see the `token` context property), but hook functions can modify this
+  to control how author IDs are allocated to users. If no author ID is
+  associated with this database key, a new author ID will be randomly generated
+  and associated with the key. For security reasons, if this is modified it
+  should be modified to not look like a valid token (see the `token` context
+  property) unless the plugin intentionally wants the user to be able to
+  impersonate another user.
+* `token`: The user-supplied token, or nullish for an anonymous user. Tokens are
+  secret values that must not be disclosed to others. If non-null, the token is
+  guaranteed to be a string with the form `t.<base64url>` where `<base64url>` is
+  any valid non-empty base64url string (RFC 4648 section 5 with padding).
+  Example: `t.twim3X2_KGiRj8cJ-3602g==`.
+* `user`: If the user has authenticated, this is an object from `settings.users`
+  (or similar from an authentication plugin). Etherpad core and all good
+  authentication plugins set the `username` property of this object to a string
+  that uniquely identifies the authenticated user. This object is nullish if the
+  user has not authenticated.
+
+Example:
+
+```javascript
+exports.getAuthorId = async (hookName, context) => {
+  const {username} = context.user || {};
+  // If the user has not authenticated, or has "authenticated" as the guest
+  // user, do the default behavior (try another plugin if any, falling through
+  // to using the token as the database key).
+  if (!username || username === 'guest') return;
+  // The user is authenticated and has a username. Give the user a stable author
+  // ID so that they appear to be the same author even after clearing cookies or
+  // accessing the pad from another device. Note that this string is guaranteed
+  // to never have the form of a valid token; without that guarantee an
+  // unauthenticated user might be able to impersonate an authenticated user.
+  context.dbKey = `username=${username}`;
+  // Return a falsy but non-undefined value to stop Etherpad from calling any
+  // more getAuthorId hook functions and look up the author ID using the
+  // username-derived database key.
+  return '';
+};
+```
+
 ## `padCreate`
 
 Called from: `src/node/db/Pad.js`

src/node/db/AuthorManager.js

@@ -21,7 +21,8 @@
 
 const db = require('./DB');
 const CustomError = require('../utils/customError');
-const randomString = require('../../static/js/pad_utils').randomString;
+const hooks = require('../../static/js/pluginfw/hooks.js');
+const {randomString, padutils: {warnDeprecated}} = require('../../static/js/pad_utils');
 
 exports.getColorPalette = () => [
   '#ffc7c7',
@@ -102,17 +103,32 @@ exports.doesAuthorExist = async (authorID) => {
 /* exported for backwards compatibility */
 exports.doesAuthorExists = exports.doesAuthorExist;
 
-/**
+const getAuthor4Token = async (token) => {
- * Returns the AuthorID for a token.
- * @param {String} token The token
- */
-exports.getAuthor4Token = async (token) => {
   const author = await mapAuthorWithDBKey('token2author', token);
 
   // return only the sub value authorID
   return author ? author.authorID : author;
 };
 
+exports.getAuthorId = async (token, user) => {
+  const context = {dbKey: token, token, user};
+  let [authorId] = await hooks.aCallFirst('getAuthorId', context);
+  if (!authorId) authorId = await getAuthor4Token(context.dbKey);
+  return authorId;
+};
+
+/**
+ * Returns the AuthorID for a token.
+ *
+ * @deprecated Use `getAuthorId` instead.
+ * @param {String} token The token
+ */
+exports.getAuthor4Token = async (token) => {
+  warnDeprecated(
+      'AuthorManager.getAuthor4Token() is deprecated; use AuthorManager.getAuthorId() instead');
+  return await getAuthor4Token(token);
+};
+
 /**
  * Returns the AuthorID for a mapper.
  * @param {String} token The mapper

src/node/db/SecurityManager.js

@@ -115,7 +115,7 @@ exports.checkAccess = async (padID, sessionCookie, token, userSettings) => {
 
   const grant = {
     accessStatus: 'grant',
-    authorID: sessionAuthorID || await authorManager.getAuthor4Token(token),
+    authorID: sessionAuthorID || await authorManager.getAuthorId(token, userSettings),
   };
 
   if (!padID.includes('$')) {