Xamarin.Authからの移行

using Newtonsoft.Json;
using Xamarin.Auth;
using Xamarin.Essentials;

public class SecureStorageAccountStore
{
    public static async Task SaveAsync(Account account, string serviceId)
    {
        // Find existing accounts for the service
        var accounts = await FindAccountsForServiceAsync(serviceId);

        // Remove existing account with Id if exists
        accounts.RemoveAny(a => a.Username == account.Username);

        // Add account we are saving
        accounts.Add(account);

        // Serialize all the accounts to javascript
        var json = JsonConvert.SerializeObject(accounts);

        // Securely save the accounts for the given service
        await SecureStorage.SetAsync(serviceId, json);
    }

    public static async Task<List<Account>> FindAccountsForServiceAsync(string serviceId)
    {
        // Get the json for accounts for the service
        var json = await SecureStorage.GetAsync(serviceId);

        try {
            // Try to return deserialized list of accounts
            return JsonConvert.DeserializeObject<List<Account>>(json);
        } catch { }

        // If this fails, return an empty list
        return new List<Account>();
    }

    public static async Task MigrateAllAccountsAsync(string serviceId, IEnumerable<Account> accountStoreAccounts)
    {
        var wasMigrated = await SecureStorage.GetAsync("XamarinAuthAccountStoreMigrated", "0");

        if (wasMigrated == "1")
            return;

        await SecureStorage.SetAsync("XamarinAuthAccountStoreMigrated", "1");

        // Just in case, look at existing 'new' accounts
        var accounts = await FindAccountsForServiceAsync(serviceId);

        foreach (var account in accountStoreAccounts) {

            // Check if the new storage already has this account
            // We don't want to overwrite it if it does
            if (accounts.Any(a => a.Username == account.Username))
                continue;   

            // Add the account we are migrating
            accounts.Add(account);
        }

        // Serialize all the accounts to javascript
        var json = JsonConvert.SerializeObject(accounts);

        // Securely save the accounts for the given service
        await SecureStorage.SetAsync(serviceId, json);
    }
}