feat: Allow init with access token

Makes it possible to just init
with an access token and a
homeserver uri and the init()
method would just call /whoami
to fetch the missing data.
Makes it easier to login with
Matrix native OIDC

lib/fake_matrix_api.dart

@@ -1352,7 +1352,7 @@ class FakeMatrixApi extends BaseClient {
             },
           },
       '/client/v3/account/whoami': (var req) =>
-          {'user_id': 'alice@example.com'},
+          {'user_id': 'alice@example.com', 'device_id': 'ABCDEFGH'},
       '/client/v3/capabilities': (var req) => {
             'capabilities': {
               'm.change_password': {'enabled': false},

lib/src/client.dart

@@ -1982,9 +1982,9 @@ class Client extends MatrixApi {
   ///
   /// Sends [LoginState.loggedIn] to [onLoginStateChanged].
   ///
-  /// If one of [newToken], [newUserID], [newDeviceID], [newDeviceName] is set then
+  /// If one of [newToken] is set, but one of [newUserID], [newDeviceID] is
-  /// all of them must be set! If you don't set them, this method will try to
+  /// null, then this method calls `/whoami` to fetch user ID and device ID
-  /// get them from the database.
+  /// and rethrows if this request fails.
   ///
   /// Set [waitForFirstSync] and [waitUntilLoadCompletedLoaded] to false to speed this
   /// up. You can then wait for `roomsLoading`, `_accountDataLoading` and
@@ -2008,16 +2008,9 @@ class Client extends MatrixApi {
     /// To track what actually happens you can set a callback here.
     void Function(InitState)? onInitStateChanged,
   }) async {
-    if ((newToken != null ||
+    if (newToken != null && homeserver == null && newHomeserver == null) {
-            newUserID != null ||
-            newDeviceID != null ||
-            newDeviceName != null) &&
-        (newToken == null ||
-            newUserID == null ||
-            newDeviceID == null ||
-            newDeviceName == null)) {
       throw ClientInitPreconditionError(
-        'If one of [newToken, newUserID, newDeviceID, newDeviceName] is set then all of them must be set!',
+        'init() can not be performed with an access token when no homeserver was specified.',
       );
     }
 
@@ -2109,6 +2102,12 @@ class Client extends MatrixApi {
         return;
       }
 
+      if (accessToken != null && (userID == null || deviceID == null)) {
+        final userInfo = await getTokenOwner();
+        _userID = userID = userInfo.userId;
+        _deviceID = userInfo.deviceId;
+      }
+
       if (accessToken == null || homeserver == null || userID == null) {
         if (legacyDatabaseBuilder != null) {
           await _migrateFromLegacyDatabase(

test/client_test.dart

@@ -524,6 +524,22 @@ void main() {
       FakeMatrixApi.currentApi?.api = oldapi!;
     });
 
+    test('init() with access token', () async {
+      final client = Client(
+        'testclient',
+        httpClient: FakeMatrixApi(),
+        database: await getDatabase(),
+      );
+      await client.init(
+        newToken: 'abcd1234',
+        newHomeserver: Uri.parse('https://fakeserver.notexisting'),
+      );
+      expect(client.isLogged(), true);
+      expect(client.userID, 'alice@example.com');
+      expect(client.deviceID, 'ABCDEFGH');
+      await client.dispose();
+    });
+
     test('Login', () async {
       matrix = Client(
         'testclient',