feat: initial fediverse registration/login
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16 changed files with 467 additions and 111 deletions
245
Foxnouns.Backend/Services/Auth/FediverseAuthService.Mastodon.cs
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245
Foxnouns.Backend/Services/Auth/FediverseAuthService.Mastodon.cs
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@ -0,0 +1,245 @@
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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 Duration = NodaTime.Duration;
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using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
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namespace Foxnouns.Backend.Services.Auth;
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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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$"{_config.BaseUrl}/auth/callback/mastodon/{instance}";
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private async Task<FediverseApplication> CreateMastodonApplicationAsync(
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string instance,
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Snowflake? existingAppId = null
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)
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{
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var resp = await _client.PostAsync(
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$"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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