accounts-multi.md

title	description
Accounts (multi-server)	Documentation of how to use the Accounts client to connect to other servers.

The accounts-base package exports two constructors, called AccountsClient and AccountsServer, which are used to create the Accounts object that is available on the client and the server, respectively.

This predefined Accounts object (along with similar convenience methods of Meteor, such as Meteor.logout) is sufficient to implement most accounts-related logic in Meteor apps. Nevertheless, these two constructors can be instantiated more than once, to create multiple independent connections between different accounts servers and their clients, in more complicated authentication situations.

{% apibox "AccountsCommon" %}

The AccountsClient and AccountsServer classes share a common superclass, AccountsCommon. Methods defined on AccountsCommon.prototype will be available on both the client and the server, via the predefined Accounts object (most common) or any custom accountsClientOrServer object created using the AccountsClient or AccountsServer constructors (less common).

Here are a few of those methods:

{% apibox "AccountsCommon#userId" %}

{% apibox "AccountsCommon#user" %}

{% apibox "AccountsCommon#config" %}

{% apibox "AccountsCommon#onLogin" %}

See description of AccountsCommon#onLoginFailure for details.

{% apibox "AccountsCommon#onLoginFailure" %}

Either the onLogin or the onLoginFailure callbacks will be called for each login attempt. The onLogin callbacks are called after the user has been successfully logged in. The onLoginFailure callbacks are called after a login attempt is denied.

These functions return an object with a single method, stop. Calling stop() unregisters the callback.

On the server, the callbacks get a single argument, the same attempt info object as validateLoginAttempt. On the client, the callback argument is an object containing a single error property set to the Error-object which was received from the failed login attempt.

{% apibox "AccountsCommon#onLogout" %}

On the server, the func callback receives a single argument with the object below. On the client, no arguments are passed.

{% dtdd name:"user" type:"Object" %} The Meteor user object of the user which just logged out. {% enddtdd %}

{% dtdd name:"connection" type:"Object" %} The connection object the request came in on. See Meteor.onConnection for details. {% enddtdd %}

{% apibox "AccountsClient" %}

At most one of options.connection and options.ddpUrl should be provided in any instantiation of AccountsClient. If neither is provided, Meteor.connection will be used as the .connection property of the AccountsClient instance.

Note that AccountsClient is currently available only on the client, due to its use of browser APIs such as window.localStorage. In principle, though, it might make sense to establish a client connection from one server to another remote accounts server. Please let us know if you find yourself needing this server-to-server functionality.

These methods are defined on AccountsClient.prototype, and are thus available only on the client:

{% apibox "AccountsClient#loggingIn" %}

{% apibox "AccountsClient#logout" %}

{% apibox "AccountsClient#logoutOtherClients" %}

{% apibox "AccountsServer" %}

These methods are defined on AccountsServer.prototype, and are thus available only on the server:

{% apibox "AccountsServer#validateNewUser" %}

This can be called multiple times. If any of the functions return false or throw an error, the new user creation is aborted. To set a specific error message (which will be displayed by accounts-ui), throw a new Meteor.Error.

Example:

// Validate username, sending a specific error message on failure.
Accounts.validateNewUser((user) => {
  if (user.username && user.username.length >= 3) {
    return true;
  } else {
    throw new Meteor.Error(403, 'Username must have at least 3 characters');
  }
});

// Validate username, without a specific error message.
Accounts.validateNewUser((user) => {
  return user.username !== 'root';
});

If the user is being created as part of a login attempt from a client (eg, calling Accounts.createUser from the client, or logging in for the first time with an external service), these callbacks are called before the Accounts.validateLoginAttempt callbacks. If these callbacks succeed but those fail, the user will still be created but the connection will not be logged in as that user.

{% apibox "AccountsServer#onCreateUser" %}

Use this when you need to do more than simply accept or reject new user creation. With this function you can programatically control the contents of new user documents.

The function you pass will be called with two arguments: options and user. The options argument comes from Accounts.createUser for password-based users or from an external service login flow. options may come from an untrusted client so make sure to validate any values you read from it. The user argument is created on the server and contains a proposed user object with all the automatically generated fields required for the user to log in, including the _id.

The function should return the user document (either the one passed in or a newly-created object) with whatever modifications are desired. The returned document is inserted directly into the Meteor.users collection.

The default create user function simply copies options.profile into the new user document. Calling onCreateUser overrides the default hook. This can only be called once.

Example:

// Support for playing D&D: Roll 3d6 for dexterity.
Accounts.onCreateUser((options, user) => {
  const customizedUser = Object.assign({
    dexterity: _.random(1, 6) + _.random(1, 6) + _.random(1, 6),
  }, user);

  // We still want the default hook's 'profile' behavior.
  if (options.profile) {
    customizedUser.profile = options.profile;
  }

  return customizedUser;
});

{% apibox "AccountsServer#validateLoginAttempt" %}

Call validateLoginAttempt with a callback to be called on login attempts. It returns an object with a single method, stop. Calling stop() unregisters the callback.

When a login attempt is made, the registered validate login callbacks are called with a single argument, the attempt info object:

{% dtdd name:"type" type:"String" %} The service name, such as "password" or "twitter". {% enddtdd %}

{% dtdd name:"allowed" type:"Boolean" %} Whether this login is allowed and will be successful (if not aborted by any of the validateLoginAttempt callbacks). False if the login will not succeed (for example, an invalid password or the login was aborted by a previous validateLoginAttempt callback). {% enddtdd %}

{% dtdd name:"error" type:"Exception" %} When allowed is false, the exception describing why the login failed. It will be a Meteor.Error for failures reported to the user (such as invalid password), and can be a another kind of exception for internal errors. {% enddtdd %}

{% dtdd name:"user" type:"Object" %} When it is known which user was attempting to login, the Meteor user object. This will always be present for successful logins. {% enddtdd %}

{% dtdd name:"connection" type:"Object" %} The connection object the request came in on. See Meteor.onConnection for details. {% enddtdd %}

{% dtdd name:"methodName" type:"String" %} The name of the Meteor method being used to login. {% enddtdd %}

{% dtdd name:"methodArguments" type:"Array" %} An array of the arguments passed to the login method. {% enddtdd %}

A validate login callback must return a truthy value for the login to proceed. If the callback returns a falsy value or throws an exception, the login is aborted. Throwing a Meteor.Error will report the error reason to the user.

All registered validate login callbacks are called, even if one of the callbacks aborts the login. The later callbacks will see the allowed field set to false since the login will now not be successful. This allows later callbacks to override an error from a previous callback; for example, you could override the "Incorrect password" error with a different message.

Validate login callbacks that aren't explicitly trying to override a previous error generally have no need to run if the attempt has already been determined to fail, and should start with

if (!attempt.allowed) {
  return false;
}

Rate Limiting

By default, there are rules added to the DDPRateLimiter that rate limit logins, new user registration and password reset calls to a limit of 5 requests per 10 seconds per session. These are a basic solution to dictionary attacks where a malicious user attempts to guess the passwords of legitimate users by attempting all possible passwords.

These rate limiting rules can be removed by calling Accounts.removeDefaultRateLimit(). Please see the DDPRateLimiter docs for more information.