feat: add some fediverse authentication code
* create applications on instances * generate authorize URLs * exchange oauth code for token and user info (untested) * recreate mastodon app on authentication failure
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246
Foxnouns.Backend/Services/FediverseAuthService.Mastodon.cs
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246
Foxnouns.Backend/Services/FediverseAuthService.Mastodon.cs
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using System.Net;
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using System.Web;
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using Foxnouns.Backend.Database;
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using Foxnouns.Backend.Database.Models;
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using Minio.DataModel.ILM;
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using Duration = NodaTime.Duration;
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using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
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namespace Foxnouns.Backend.Services;
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public partial class FediverseAuthService
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{
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private string MastodonRedirectUri(string instance) =>
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$"{_config.BaseUrl}/auth/login/mastodon/{instance}";
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private async Task<FediverseApplication> CreateMastodonApplicationAsync(
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string instance,
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Snowflake? existingAppId = null
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)
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{
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var resp = await _client.PostAsync(
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$"https://{instance}/api/v1/apps",
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new FormUrlEncodedContent(
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new Dictionary<string, string>
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{
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{ "client_name", $"pronouns.cc (+{_config.BaseUrl})" },
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{ "redirect_uris", MastodonRedirectUri(instance) },
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{ "scope", "read:accounts" },
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{ "website", _config.BaseUrl },
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}
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)
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);
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resp.EnsureSuccessStatusCode();
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var mastodonApp = await resp.Content.ReadFromJsonAsync<PartialMastodonApplication>();
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if (mastodonApp == null)
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throw new FoxnounsError(
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$"Application created on Mastodon-compatible instance {instance} was null"
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);
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var token = await GetMastodonAppTokenAsync(
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instance,
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mastodonApp.ClientId,
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mastodonApp.ClientSecret
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);
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FediverseApplication app;
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if (existingAppId == null)
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{
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app = new FediverseApplication
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{
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Id = existingAppId ?? _snowflakeGenerator.GenerateSnowflake(),
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ClientId = mastodonApp.ClientId,
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ClientSecret = mastodonApp.ClientSecret,
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Domain = instance,
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InstanceType = FediverseInstanceType.MastodonApi,
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AccessToken = token,
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TokenValidUntil = _clock.GetCurrentInstant() + Duration.FromDays(60),
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};
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_db.Add(app);
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}
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else
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{
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app =
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await _db.FediverseApplications.FindAsync(existingAppId)
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?? throw new FoxnounsError($"Existing app with ID {existingAppId} was null");
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app.ClientId = mastodonApp.ClientId;
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app.ClientSecret = mastodonApp.ClientSecret;
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app.InstanceType = FediverseInstanceType.MastodonApi;
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app.AccessToken = null;
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app.TokenValidUntil = null;
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}
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await _db.SaveChangesAsync();
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return app;
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}
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private async Task<FediverseUser> GetMastodonUserAsync(FediverseApplication app, string code)
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{
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var tokenResp = await _client.PostAsync(
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MastodonTokenUri(app.Domain),
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new FormUrlEncodedContent(
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new Dictionary<string, string>
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{
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{ "grant_type", "authorization_code" },
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{ "code", code },
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{ "scope", "read:accounts" },
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{ "client_id", app.ClientId },
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{ "client_secret", app.ClientSecret },
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{ "redirect_uri", MastodonRedirectUri(app.Domain) },
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}
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)
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);
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if (tokenResp.StatusCode == HttpStatusCode.Unauthorized)
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{
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throw new FoxnounsError($"Application for instance {app.Domain} was invalid");
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}
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tokenResp.EnsureSuccessStatusCode();
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var token = (
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await tokenResp.Content.ReadFromJsonAsync<MastodonTokenResponse>()
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)?.AccessToken;
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if (token == null)
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{
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throw new FoxnounsError($"Token response from instance {app.Domain} was invalid");
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}
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var req = new HttpRequestMessage(HttpMethod.Get, MastodonCurrentUserUri(app.Domain));
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req.Headers.Add("Authorization", $"Bearer {token}");
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var currentUserResp = await _client.SendAsync(req);
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currentUserResp.EnsureSuccessStatusCode();
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var user = await currentUserResp.Content.ReadFromJsonAsync<FediverseUser>();
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if (user == null)
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{
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throw new FoxnounsError($"User response from instance {app.Domain} was invalid");
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}
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return user;
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}
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private record MastodonTokenResponse([property: J("access_token")] string AccessToken);
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// TODO: Mastodon's OAuth documentation doesn't specify a "state" parameter. that feels... wrong
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// https://docs.joinmastodon.org/methods/oauth/
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private async Task<string> GenerateMastodonAuthUrlAsync(FediverseApplication app)
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{
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try
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{
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await ValidateMastodonAppAsync(app);
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}
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catch (FoxnounsError.RemoteAuthError e)
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{
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_logger.Error(
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e,
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"Error validating app token for {AppId} on {Instance}",
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app.Id,
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app.Domain
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);
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app = await CreateMastodonApplicationAsync(app.Domain, existingAppId: app.Id);
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}
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return $"https://{app.Domain}/oauth/authorize?response_type=code"
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+ $"&client_id={app.ClientId}"
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+ $"&scope={HttpUtility.UrlEncode("read:accounts")}"
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+ $"&redirect_uri={HttpUtility.UrlEncode(MastodonRedirectUri(app.Domain))}";
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}
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private async Task ValidateMastodonAppAsync(FediverseApplication app)
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{
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// If we don't have an access token stored, or it's too old, get one
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// When doing this we don't need to fetch the application info
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if (app.AccessToken == null || app.TokenValidUntil < _clock.GetCurrentInstant())
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{
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_logger.Debug(
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"Application {AppId} on instance {Instance} has no valid token, fetching it",
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app.Id,
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app.Domain
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);
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app.AccessToken = await GetMastodonAppTokenAsync(
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app.Domain,
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app.ClientId,
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app.ClientSecret
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);
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app.TokenValidUntil = _clock.GetCurrentInstant() + Duration.FromDays(60);
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_db.Update(app);
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await _db.SaveChangesAsync();
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return;
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}
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_logger.Debug(
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"Checking whether application {AppId} on instance {Instance} is still valid",
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app.Id,
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app.Domain
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);
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var req = new HttpRequestMessage(HttpMethod.Get, MastodonCurrentAppUri(app.Domain));
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req.Headers.Add("Authorization", $"Bearer {app.AccessToken}");
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var resp = await _client.SendAsync(req);
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if (!resp.IsSuccessStatusCode)
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{
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var error = await resp.Content.ReadAsStringAsync();
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throw new FoxnounsError.RemoteAuthError(
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"Verifying app credentials returned an error",
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error
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);
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}
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}
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private async Task<string> GetMastodonAppTokenAsync(
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string instance,
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string clientId,
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string clientSecret
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)
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{
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var resp = await _client.PostAsync(
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MastodonTokenUri(instance),
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new FormUrlEncodedContent(
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new Dictionary<string, string>
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{
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{ "grant_type", "client_credentials" },
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{ "client_id", clientId },
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{ "client_secret", clientSecret },
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}
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)
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);
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if (!resp.IsSuccessStatusCode)
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{
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var error = await resp.Content.ReadAsStringAsync();
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throw new FoxnounsError.RemoteAuthError(
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"Requesting app token returned an error",
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error
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);
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}
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var token = (await resp.Content.ReadFromJsonAsync<MastodonTokenResponse>())?.AccessToken;
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if (token == null)
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{
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throw new FoxnounsError($"Token response from instance {instance} was invalid");
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}
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return token;
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}
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private static string MastodonTokenUri(string instance) => $"https://{instance}/oauth/token";
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private static string MastodonCurrentUserUri(string instance) =>
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$"https://{instance}/api/v1/accounts/verify_credentials";
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private static string MastodonCurrentAppUri(string instance) =>
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$"https://{instance}/api/v1/apps/verify_credentials";
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private record PartialMastodonApplication(
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[property: J("name")] string Name,
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[property: J("client_id")] string ClientId,
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[property: J("client_secret")] string ClientSecret
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);
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}
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162
Foxnouns.Backend/Services/FediverseAuthService.cs
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162
Foxnouns.Backend/Services/FediverseAuthService.cs
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@ -0,0 +1,162 @@
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using Foxnouns.Backend.Database;
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using Foxnouns.Backend.Database.Models;
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using Microsoft.EntityFrameworkCore;
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using NodaTime;
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using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
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namespace Foxnouns.Backend.Services;
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public partial class FediverseAuthService
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{
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private const string NodeInfoRel = "http://nodeinfo.diaspora.software/ns/schema/2.0";
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private readonly ILogger _logger;
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private readonly HttpClient _client;
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private readonly DatabaseContext _db;
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private readonly Config _config;
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private readonly ISnowflakeGenerator _snowflakeGenerator;
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private readonly IClock _clock;
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public FediverseAuthService(
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ILogger logger,
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Config config,
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DatabaseContext db,
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ISnowflakeGenerator snowflakeGenerator,
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IClock clock
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)
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{
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_config = config;
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_db = db;
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_snowflakeGenerator = snowflakeGenerator;
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_clock = clock;
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_logger = logger.ForContext<FediverseAuthService>();
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_client = new HttpClient();
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_client.DefaultRequestHeaders.Remove("User-Agent");
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_client.DefaultRequestHeaders.Remove("Accept");
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_client.DefaultRequestHeaders.Add("User-Agent", $"pronouns.cc/{BuildInfo.Version}");
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_client.DefaultRequestHeaders.Add("Accept", "application/json");
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}
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public async Task<string> GenerateAuthUrlAsync(string instance)
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{
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var app = await GetApplicationAsync(instance);
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return await GenerateAuthUrlAsync(app);
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}
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public async Task<FediverseUser> GetRemoteFediverseUserAsync(string instance, string code)
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{
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var app = await GetApplicationAsync(instance);
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return await GetRemoteUserAsync(app, code);
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}
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// thank you, gargron and syuilo, for agreeing on a name for *once* in your lives,
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// and having both mastodon and misskey use "username" in the self user response
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public record FediverseUser(
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[property: J("id")] string Id,
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[property: J("username")] string Username
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);
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private async Task<FediverseApplication> GetApplicationAsync(string instance)
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{
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var app = await _db.FediverseApplications.FirstOrDefaultAsync(a => a.Domain == instance);
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if (app != null)
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return app;
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_logger.Debug("No application for fediverse instance {Instance}, creating it", instance);
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var softwareName = await GetSoftwareNameAsync(instance);
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if (IsMastodonCompatible(softwareName))
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{
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return await CreateMastodonApplicationAsync(instance);
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}
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throw new NotImplementedException();
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}
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private async Task<string> GetSoftwareNameAsync(string instance)
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{
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_logger.Debug("Requesting software name for fediverse instance {Instance}", instance);
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var wellKnownResp = await _client.GetAsync(
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new Uri($"https://{instance}/.well-known/nodeinfo")
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);
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wellKnownResp.EnsureSuccessStatusCode();
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var wellKnown = await wellKnownResp.Content.ReadFromJsonAsync<WellKnownResponse>();
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var nodeInfoUrl = wellKnown?.Links.FirstOrDefault(l => l.Rel == NodeInfoRel)?.Href;
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if (nodeInfoUrl == null)
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{
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throw new FoxnounsError(
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$".well-known/nodeinfo response for instance {instance} was invalid, no nodeinfo link"
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);
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}
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var nodeInfoResp = await _client.GetAsync(nodeInfoUrl);
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nodeInfoResp.EnsureSuccessStatusCode();
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var nodeInfo = await nodeInfoResp.Content.ReadFromJsonAsync<PartialNodeInfo>();
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return nodeInfo?.Software.Name
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?? throw new FoxnounsError(
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$"Nodeinfo response for instance {instance} was invalid, no software name"
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);
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}
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private async Task<string> GenerateAuthUrlAsync(FediverseApplication app) =>
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app.InstanceType switch
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{
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FediverseInstanceType.MastodonApi => await GenerateMastodonAuthUrlAsync(app),
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FediverseInstanceType.MisskeyApi => throw new NotImplementedException(),
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_ => throw new ArgumentOutOfRangeException(nameof(app), app.InstanceType, null),
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};
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private async Task<FediverseUser> GetRemoteUserAsync(FediverseApplication app, string code) =>
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app.InstanceType switch
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{
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FediverseInstanceType.MastodonApi => await GetMastodonUserAsync(app, code),
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FediverseInstanceType.MisskeyApi => throw new NotImplementedException(),
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_ => throw new ArgumentOutOfRangeException(nameof(app), app.InstanceType, null),
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};
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private static readonly string[] MastodonSoftwareNames =
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[
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"mastodon",
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"hometown",
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"akkoma",
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"pleroma",
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"iceshrimp.net",
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"iceshrimp",
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"gotosocial",
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"pixelfed",
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];
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private static readonly string[] MisskeySoftwareNames =
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[
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"misskey",
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"foundkey",
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"calckey",
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"firefish",
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"sharkey",
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];
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private static bool IsMastodonCompatible(string softwareName) =>
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MastodonSoftwareNames.Any(n =>
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string.Equals(softwareName, n, StringComparison.InvariantCultureIgnoreCase)
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);
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private static bool IsMisskeyCompatible(string softwareName) =>
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MisskeySoftwareNames.Any(n =>
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string.Equals(softwareName, n, StringComparison.InvariantCultureIgnoreCase)
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);
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private record WellKnownResponse([property: J("links")] WellKnownLink[] Links);
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private record WellKnownLink(
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[property: J("rel")] string Rel,
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[property: J("href")] string Href
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);
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private record PartialNodeInfo([property: J("software")] NodeInfoSoftware Software);
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private record NodeInfoSoftware([property: J("name")] string Name);
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}
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