AccountAuthentication with Single Activity Application

I tried to create authentication with my server for my application using AbstractAccountAuthenticator and AccountManager. I am also trying to create Single Activity Application. addAccount My problem is that I need to give an intention in "addAccount() in AbstractAccountAuthenticator" to run AuthActivity. How can I give the intention simply to launch a fragment or something like that to serve these purposes? What other options may be for implementing such authentication in Single Activity Application?

My idea was to create an intention to launch MainActivity and already with the help of Bundle start fragment where manage the result of activity.

Classic implementation with Multi Activity Application

@Override
    public Bundle addAccount(AccountAuthenticatorResponse response, String accountType, String authTokenType, String[] requiredFeatures, Bundle options) throws NetworkErrorException {
        Log.d("udinic", TAG + "> addAccount");

        final Intent intent = new Intent(mContext, AuthenticatorActivity.class);
        intent.putExtra(AuthenticatorActivity.ARG_ACCOUNT_TYPE, accountType);
        intent.putExtra(AuthenticatorActivity.ARG_AUTH_TYPE, authTokenType);
        intent.putExtra(AuthenticatorActivity.ARG_IS_ADDING_NEW_ACCOUNT, true);
        intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response);

        final Bundle bundle = new Bundle();
        bundle.putParcelable(AccountManager.KEY_INTENT, intent);
        return bundle;
    }

    @Override
    public Bundle getAuthToken(AccountAuthenticatorResponse response, Account account, String authTokenType, Bundle options) throws NetworkErrorException {

        Log.d("udinic", TAG + "> getAuthToken");

        // If the caller requested an authToken type we don't support, then
        // return an error
        if (!authTokenType.equals(AccountGeneral.AUTHTOKEN_TYPE_READ_ONLY) && !authTokenType.equals(AccountGeneral.AUTHTOKEN_TYPE_FULL_ACCESS)) {
            final Bundle result = new Bundle();
            result.putString(AccountManager.KEY_ERROR_MESSAGE, "invalid authTokenType");
            return result;
        }

        // Extract the username and password from the Account Manager, and ask
        // the server for an appropriate AuthToken.
        final AccountManager am = AccountManager.get(mContext);

        String authToken = am.peekAuthToken(account, authTokenType);

        Log.d("udinic", TAG + "> peekAuthToken returned - " + authToken);

        // Lets give another try to authenticate the user
        if (TextUtils.isEmpty(authToken)) {
            final String password = am.getPassword(account);
            if (password != null) {
                try {
                    Log.d("udinic", TAG + "> re-authenticating with the existing password");
                    authToken = sServerAuthenticate.userSignIn(account.name, password, authTokenType);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }

        // If we get an authToken - we return it
        if (!TextUtils.isEmpty(authToken)) {
            final Bundle result = new Bundle();
            result.putString(AccountManager.KEY_ACCOUNT_NAME, account.name);
            result.putString(AccountManager.KEY_ACCOUNT_TYPE, account.type);
            result.putString(AccountManager.KEY_AUTHTOKEN, authToken);
            return result;
        }

        // If we get here, then we couldn't access the user's password - so we
        // need to re-prompt them for their credentials. We do that by creating
        // an intent to display our AuthenticatorActivity.
        final Intent intent = new Intent(mContext, AuthenticatorActivity.class);
        intent.putExtra(AccountManager.KEY_ACCOUNT_AUTHENTICATOR_RESPONSE, response);
        intent.putExtra(AuthenticatorActivity.ARG_ACCOUNT_TYPE, account.type);
        intent.putExtra(AuthenticatorActivity.ARG_AUTH_TYPE, authTokenType);
        intent.putExtra(AuthenticatorActivity.ARG_ACCOUNT_NAME, account.name);
        final Bundle bundle = new Bundle();
        bundle.putParcelable(AccountManager.KEY_INTENT, intent);
        return bundle;
    }


    @Override
    public String getAuthTokenLabel(String authTokenType) {
        if (AUTHTOKEN_TYPE_FULL_ACCESS.equals(authTokenType))
            return AUTHTOKEN_TYPE_FULL_ACCESS_LABEL;
        else if (AUTHTOKEN_TYPE_READ_ONLY.equals(authTokenType))
            return AUTHTOKEN_TYPE_READ_ONLY_LABEL;
        else
            return authTokenType + " (Label)";
    }