decePubClient/Services/TokenAuthStateProvider.cs

using Blazored.LocalStorage;

using decePubClient.Models;

using Microsoft.AspNetCore.Components.Authorization;

using PrivaPub.ClientModels;
using PrivaPub.ClientModels.User;

using System.Security.Claims;

namespace decePubClient.Services
{
	/// <summary>
	/// The session (AuthData in localStorage, cached in memory) and the authentication state built from it. It only
	/// stores and hands out tokens; signing in, exchanging and revoking them is AuthService's job.
	/// </summary>
	public class TokenAuthStateProvider(ILocalStorageService storage, ILogger<TokenAuthStateProvider> logger)
		: AuthenticationStateProvider
	{
		/// <summary>The claim naming the persona the client acts as (an avatar id).</summary>
		public const string PersonaClaim = "persona";

		AuthData authData;
		bool loaded;

		/// <summary>The stored session, or an empty one.</summary>
		public async Task<AuthData> GetAuthData(CancellationToken cancellationToken = default)
		{
			if (loaded)
				return authData ?? new();

			authData = await storage.GetItemAsync<AuthData>(nameof(AuthData), cancellationToken);
			loaded = true;
			return authData ?? new();
		}

		/// <summary>The root's JWT while it is still valid, otherwise null.</summary>
		public async Task<string> GetToken(CancellationToken cancellationToken = default)
		{
			var session = await GetAuthData(cancellationToken);
			if (string.IsNullOrEmpty(session.Token) || session.TokenExpiration is not { } expiration || expiration <= DateTime.UtcNow.Ticks)
				return null;
			return session.Token;
		}

		/// <summary>The current persona's Mastodon token, or null when the persona has none yet.</summary>
		public async Task<string> GetPersonaToken(CancellationToken cancellationToken = default)
		{
			var session = await GetAuthData(cancellationToken);
			if (session.PersonaId is null)
				return null;
			return session.PersonaTokens.GetValueOrDefault(session.PersonaId);
		}

		public async Task<bool> IsAuthenticatedAsync(CancellationToken cancellationToken = default) =>
			await GetToken(cancellationToken) is not null;

		/// <summary>Starts or renews the session with a JWT from login or sniff/again; persona tokens are kept.</summary>
		public async Task SetSession(JwtUser jwtUser, CancellationToken cancellationToken = default)
		{
			var session = await GetAuthData(cancellationToken);
			session.Token = jwtUser.Token;
			session.TokenExpiration = jwtUser.Expiration;
			session.TokenIssuedAt = DateTime.UtcNow.Ticks;
			session.UserName = jwtUser.Username;
			session.Policies = jwtUser.Policies ?? [];
			if (jwtUser.UserSettings?.LanguageCode is { Length: > 0 } language)
				session.CurrentLanguageCode = language;
			await Save(session, cancellationToken);
		}

		/// <summary>Makes the persona current, remembering its token when one is given.</summary>
		public async Task SetPersona(string personaId, string token = default, CancellationToken cancellationToken = default)
		{
			var session = await GetAuthData(cancellationToken);
			session.PersonaId = personaId;
			if (token is not null)
				session.PersonaTokens[personaId] = token;
			await Save(session, cancellationToken);
		}

		/// <summary>Drops a persona's token that PrivaPub no longer accepts.</summary>
		public async Task ForgetPersonaToken(string personaId, CancellationToken cancellationToken = default)
		{
			var session = await GetAuthData(cancellationToken);
			if (!session.PersonaTokens.Remove(personaId))
				return;
			await Save(session, cancellationToken);
		}

		public async Task LogoutAsync(CancellationToken cancellationToken = default)
		{
			logger.LogInformation($"set null({nameof(LogoutAsync)})");
			authData = null;
			loaded = true;
			await storage.RemoveItemAsync(nameof(AuthData), cancellationToken);

			NotifyAuthenticationStateChanged(GetAuthenticationStateAsync());
		}

		public override async Task<AuthenticationState> GetAuthenticationStateAsync()
		{
			var token = await GetToken();
			if (token is null)
				return new(new());

			var session = await GetAuthData();
			var claims = new List<Claim> { new(ClaimTypes.Name, session.UserName ?? string.Empty) };
			foreach (var policy in new[] { Policies.IsUser, Policies.IsModerator, Policies.IsAdmin })
				claims.Add(new(policy, session.Policies.Contains(policy) ? "true" : "false"));
			if (session.PersonaId is not null)
				claims.Add(new(PersonaClaim, session.PersonaId));

			return new(new(new ClaimsIdentity(claims, "jwt")));
		}

		async Task Save(AuthData session, CancellationToken cancellationToken)
		{
			authData = session;
			loaded = true;
			await storage.SetItemAsync(nameof(AuthData), session, cancellationToken);
			NotifyAuthenticationStateChanged(GetAuthenticationStateAsync());
		}
	}
}