Custom overrides

It is recommended to use the serverpod_auth_idp package but if you have special requirements not fulfilled by it, you can implement your authentication module. Serverpod is designed to make it easy to add custom authentication overrides.

Server setup

When running a custom auth integration it is up to you to build the authentication model and issuing auth tokens.

Token validation

The token validation is performed by providing a custom AuthenticationHandler callback when initializing Serverpod. The callback should return an AuthenticationInfo object if the token is valid, otherwise null.

// Initialize Serverpod and connect it with your generated code.
final pod = Serverpod(
  args,
  Protocol(),
  Endpoints(),
  authenticationHandler: (Session session, String token) async {
    /// Custom validation handler
    if (token != 'valid') return null;

    return AuthenticationInfo(1, <Scope>{});
  },
);

In the above example, the authenticationHandler callback is overridden with a custom validation method. The method returns an AuthenticationInfo object with userIdentifier "1" and no scopes if the token is the literal "valid", otherwise null.

note

The userIdentifier passed to the AuthenticationInfo constructor, as the first parameter, will always be converted to a String and thus stored internally. Since the default implementation uses UuidValue for the users, there is a convenience getter userId, which returns the UuidValue value.

note

In the authenticationHandler callback the authenticated field on the session will always be null as it is the authenticationHandler that figures out who the user is.

info

By specifying the optional authId field in the AuthenticationInfo object you can link the user to a specific authentication id. This is useful when revoking authentication for a specific device.

Scopes

The scopes returned from the authenticationHandler is used to grant access to scope restricted endpoints. The Scope class is a simple wrapper around a nullable String in dart. This means that you can format your scopes however you want as long as they are in a String format.

Normally if you implement a JWT you would store the scopes inside the token. When extracting them all you have to do is convert the String stored in the token into a Scope object by calling the constructor.

List<String> scopes = extractScopes(token);
Set<Scope> userScopes = scopes.map((scope) => Scope(scope)).toSet();

Handling revoked authentication

When a user's authentication is revoked, the server must be notified to respect the changes (e.g. to close method streams). Invoke the session.messages.authenticationRevoked method and raise the appropriate event to notify the server.

var userId = 1;
var revokedScopes = ['write'];
var message = RevokedAuthenticationScope(
  scopes: revokedScopes,
);

await session.messages.authenticationRevoked(
  userId,
  message,
);

Parameters

• userId - The user id belonging to the AuthenticationInfo object to be revoked.
• message - The revoked authentication event message. See below for the different type of messages.

Revoked authentication messages

There are three types of RevokedAuthentication messages that are used to specify the extent of the authentication revocation:

Message type	Description
RevokedAuthenticationUser	All authentication is revoked for a user.
RevokedAuthenticationAuthId	A single authentication id is revoked for the user. This should match the authId field in the AuthenticationInfo object.
RevokedAuthenticationScope	List of scopes that have been revoked for a user.

Each message type provides a tailored approach to revoke authentication based on different needs.

Send token to client

You are responsible for implementing the endpoints to authenticate/authorize the user. But as an example such an endpoint could look like the following.

class UserEndpoint extends Endpoint {
  Future<LoginResponse> login(
    Session session,
    String username,
    String password,
  ) async {
    var identifier = authenticateUser(session, username, password);
    if (identifier == null) return null;

    return issueMyToken(identifier, scopes: {});
  }
}

In the above example, the login method authenticates the user and creates an auth token. The token is then returned to the client.

Client setup

Enabling authentication in the client is as simple as configuring an auth key provider. If an auth key provider is configured, the client will automatically query the provider for an authentication header value and include it in communication with the server.

Configure auth key provider

Auth key providers need to implement the ClientAuthKeyProvider interface. The provider is configured when creating the client by passing it as the named parameter authKeyProvider. If no provider is configured, the client will not include authentication headers in requests to the server.

import 'package:serverpod_client/serverpod_client.dart';

class SimpleAuthKeyProvider implements ClientAuthKeyProvider {
  String? _key;

  @override
  Future<String?> get authHeaderValue async {
    if (_key == null) return null;
    return wrapAsBasicAuthHeaderValue(_key!);
  }

  Future<void> put(String key) async {
    _key = key;
  }

  Future<void> remove() async {
    _key = null;
  }
}

var client = Client('http://$localhost:8080/')
  ..authKeyProvider = SimpleAuthKeyProvider()
  ..connectivityMonitor = FlutterConnectivityMonitor();

In the above example, the SimpleAuthKeyProvider is configured as the client's authentication key provider. The SimpleAuthKeyProvider stores the token in memory and wraps it as a Basic auth header value using the wrapAsBasicAuthHeaderValue utility function.

info

The SimpleAuthKeyProvider is not practical and should only be used for testing. A secure implementation of the auth key provider is available in the serverpod_auth_core_flutter package. It provides safe, persistent storage for the auth token.

The auth key provider is then available through the client's authKeyProvider field. It is useful to create a getter for it to avoid unnecessary casting.

var authProvider = client.authKeyProvider as SimpleAuthKeyProvider;

It is the responsibility of the client to store the token in the auth key provider.

Authentication schemes

By default Serverpod will pass the authentication token from client to server in accordance with the HTTP authorization header standard with the basic scheme name and encoding. This is securely transferred as the connection is TLS encrypted.

The default implementation encodes and wraps the user-provided token in a basic scheme which is automatically unwrapped on the server side before being handed to the user-provided authentication handler described above.

In other words the default transport implementation is "invisible" to user code.

Implementing your own authentication scheme

If you are implementing your own authentication and are using the basic scheme, note that this is supported but will be automatically unwrapped i.e. decoded on the server side before being handed to your AuthenticationHandler implementation. It will in this case receive the decoded auth key value after the basic scheme name.

If you are implementing a different authentication scheme, for example OAuth2 using bearer tokens, you should return the appropriate header value from the authHeaderValue getter of your ClientAuthKeyProvider implementation. You can use the utility functions wrapAsBasicAuthHeaderValue or wrapAsBearerAuthHeaderValue to format the token correctly.

You will also need to implement the AuthenticationHandler accordingly, in order to process that header value server-side.

The header value must be compliant with the HTTP header format defined in RFC 9110 HTTP Semantics, 11.6.2. Authorization. See:

• HTTP Authorization header
• RFC 9110, 11.6.2. Authorization

An approach to adding OAuth handling might make changes to the above code akin to the following.

Client side:

import 'package:serverpod_client/serverpod_client.dart';

class MyOAuthKeyProvider implements ClientAuthKeyProvider {
  String? _key;

  @override
  Future<String?> get authHeaderValue async {
    if (_key == null) return null;
    return wrapAsBearerAuthHeaderValue(myBearerTokenObtainer(_key!));
  }

  Future<void> put(String key) async {
    _key = key;
  }

  Future<void> remove() async {
    _key = null;
  }
}

var client = Client('http://$localhost:8080/')
  ..authKeyProvider = MyOAuthKeyProvider()
  ..connectivityMonitor = FlutterConnectivityMonitor();

Server side:

// Initialize Serverpod and connect it with your generated code.
final pod = Serverpod(
  args,
  Protocol(),
  Endpoints(),
  authenticationHandler: (Session session, String token) async {
    /// Bearer token validation handler
    var (uid, scopes) = myBearerTokenValidator(token)
    if (uid == null) return null;

    return AuthenticationInfo(uid, scopes);
  },
);