Account Handler

Overview

Account Handler manages the state of a single Fuchsia account (and its personae) on a Fuchsia device. It also provides access to authentication tokens for the Service Provider accounts associated with the Fuchsia account.

Account Handler component instances come in two variants, one for persistent, and one for ephemeral accounts. Both are launched by Account Manager and implement the fuchsia.identity.internal.AccountHandlerControl FIDL protocols so they may be controlled by Account Manager. Each Account Handler component instance is responsible for handling a single Fuchsia account. A persistent account handler only accesses the persistent storage for that one account. An ephemeral account handler has no persistent storage priveleges at all.

Account Handler also implements the fuchsia.identity.account.Account and fuchsia.identity.account.Persona FIDL protocols. These protocols are not discoverable; Account channels may only be obtained through Account Manager and Persona channels may only be obtained from an Account channel.

Key Dependencies

• /identity/lib/account_common - Account Handler uses error and identifier definitions from this crate
• /identity/lib/identity_common - Account Handler uses the TaskGroup type from this crate
• /identity/lib/token_manager - Account Manager uses the TokenManager library to perform the authentication token management and implement the fuchsia.auth.TokenManager FIDL protocol
• fuchsia.stash.Store - The persistent Account Handler uses stash to store pre-authentication data such as what authentication mechanisms are enrolled.

Design

AccountHandler implements the fuchsia.identity.internal.AccountHandlerControl FIDL protocol. The crate‘s main function creates a single instance of AccountHandler and uses it to handle all incoming requests. An AccountHandlerContext is supplied in Account Handler’s namespace as it is launched. The LocalAccountId is also supplied to the Account Handler at launch time, but is passed through a flag instead, and parsed by in the main program entry point.

The AccountHandlerControl protocol drives a state machine in the Account Handler, starting in an Uninitialized state. Once an account is unlocked or created, the AccountHandler is considered Initialized. When initialized, the Account serves subsequent AccountHandlerControl.GetAccount calls. Notably, the AccountHandler can also be in the Locked state, where the Account is not available. Unlocking may involve an authentication attempt if the account was enrolled with an authentication mechanism upon creation.

Account implements the fuchsia.identity.account.Account FIDL protocol and stores an instance of the Persona struct representing the default Persona. When a persistent Account is constructed, it manages a database file using a StoredAccount. The Account also stores an instance of TokenManager, supplied with a path to the token database upon creation (if the account is persistent).

Persona implements the fuchsia.identity.account.Persona FIDL protocol.

StoredAccount implements JSON serialization and deserialization of account metadata.

Future Work

The Account Handler is not yet fully complete. In particular the change listener protocols and local authentication state are not finished.

Currently Account Handler (and the associated FIDL protocol) only handles a single persona for each account. Eventually we will support the creation and management of multiple personae.