Token Manager Factory is a component used to manage authentication tokens for Fuchsia. It maintains databases containing long-lived tokens for sets of service provider accounts, where each database relates to a single user of the device where the notion of user is defined by the client of Token Manager Factory.
In most Fuchsia configurations authentication tokens are managed through Account Manager rather than Token Manager Factory, but Token Manager Factory is still required for some fallback cases.
TokenManagerFactory implements the fuchsia.auth.TokenManagerFactory FIDL protocol. The crate's main function creates a single instance of this struct and uses it to handle all incoming requests. TokenManagerFactory maintains a single instance of AuthProviderSupplier and a map from user to instances of token_manager::TokenManager, creating new entries in the map on the first request for each user.
AuthProviderSupplier implements the token_manager::AuthProviderSupplier trait, maintaining a map from auth_provider_type to instances of token_manager::AuthProviderConnection in order to lazily launch auth provider components on first request.
Once the current fallback cases requiring Token Manager Factory have been resolved to use Account Manager, Token Manager Factory will either be removed entirely or downscoped to remove the multi-user support and retained for devices that do not need the full multi-user Fuchsia account system.
Currently the set of Auth Providers known to Token Manager Factory must be passed by the caller in every request to create a Token Manager channel and these must be consistent across calls. If Token Manager Factory is not removed entirely, in the future it will move to a config file based configuration that will let different build configurations install different Auth Providers and remove the need for clients to supply configuration. In the longer term we will support dynamic addition of Auth Providers at runtime.