feat: initial fediverse registration/login

Foxnouns.Backend/Controllers/Authentication/AuthController.cs

@@ -50,17 +50,6 @@ public class AuthController(
         Instant ExpiresAt
     );
 
-    public record CallbackResponse(
-        bool HasAccount,
-        [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)] string? Ticket,
-        [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
-            string? RemoteUsername,
-        [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
-            UserRendererService.UserResponse? User,
-        [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)] string? Token,
-        [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)] Instant? ExpiresAt
-    );
-
     public record OauthRegisterRequest(string Ticket, string Username);
 
     public record CallbackRequest(string Code, string State);
@@ -77,3 +66,13 @@ public class AuthController(
         return NoContent();
     }
 }
+
+public record CallbackResponse(
+    bool HasAccount,
+    [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)] string? Ticket,
+    [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)] string? RemoteUsername,
+    [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)]
+        UserRendererService.UserResponse? User,
+    [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)] string? Token,
+    [property: JsonProperty(NullValueHandling = NullValueHandling.Ignore)] Instant? ExpiresAt
+);

Foxnouns.Backend/Controllers/Authentication/DiscordAuthController.cs

@@ -2,6 +2,7 @@ using Foxnouns.Backend.Database;
 using Foxnouns.Backend.Database.Models;
 using Foxnouns.Backend.Extensions;
 using Foxnouns.Backend.Services;
+using Foxnouns.Backend.Services.Auth;
 using Foxnouns.Backend.Utils;
 using JetBrains.Annotations;
 using Microsoft.AspNetCore.Mvc;
@@ -14,20 +15,16 @@ namespace Foxnouns.Backend.Controllers.Authentication;
 public class DiscordAuthController(
     [UsedImplicitly] Config config,
     ILogger logger,
-    IClock clock,
     DatabaseContext db,
     KeyCacheService keyCacheService,
     AuthService authService,
-    RemoteAuthService remoteAuthService,
-    UserRendererService userRenderer
+    RemoteAuthService remoteAuthService
 ) : ApiControllerBase
 {
     private readonly ILogger _logger = logger.ForContext<DiscordAuthController>();
 
     [HttpPost("callback")]
-    // TODO: duplicating attribute doesn't work, find another way to mark both as possible response
-    // leaving it here for documentation purposes
-    [ProducesResponseType<AuthController.CallbackResponse>(StatusCodes.Status200OK)]
+    [ProducesResponseType<CallbackResponse>(StatusCodes.Status200OK)]
     public async Task<IActionResult> CallbackAsync([FromBody] AuthController.CallbackRequest req)
     {
         CheckRequirements();
@@ -36,7 +33,7 @@ public class DiscordAuthController(
         var remoteUser = await remoteAuthService.RequestDiscordTokenAsync(req.Code);
         var user = await authService.AuthenticateUserAsync(AuthType.Discord, remoteUser.Id);
         if (user != null)
-            return Ok(await GenerateUserTokenAsync(user));
+            return Ok(await authService.GenerateUserTokenAsync(user));
 
         _logger.Debug(
             "Discord user {Username} ({Id}) authenticated with no local account",
@@ -52,7 +49,7 @@ public class DiscordAuthController(
         );
 
         return Ok(
-            new AuthController.CallbackResponse(
+            new CallbackResponse(
                 HasAccount: false,
                 Ticket: ticket,
                 RemoteUsername: remoteUser.Username,
@@ -94,42 +91,7 @@ public class DiscordAuthController(
             remoteUser.Username
         );
 
-        return Ok(await GenerateUserTokenAsync(user));
-    }
-
-    private async Task<AuthController.CallbackResponse> GenerateUserTokenAsync(
-        User user,
-        CancellationToken ct = default
-    )
-    {
-        var frontendApp = await db.GetFrontendApplicationAsync(ct);
-        _logger.Debug("Logging user {Id} in with Discord", user.Id);
-
-        var (tokenStr, token) = authService.GenerateToken(
-            user,
-            frontendApp,
-            ["*"],
-            clock.GetCurrentInstant() + Duration.FromDays(365)
-        );
-        db.Add(token);
-
-        _logger.Debug("Generated token {TokenId} for {UserId}", user.Id, token.Id);
-
-        await db.SaveChangesAsync(ct);
-
-        return new AuthController.CallbackResponse(
-            HasAccount: true,
-            Ticket: null,
-            RemoteUsername: null,
-            User: await userRenderer.RenderUserAsync(
-                user,
-                selfUser: user,
-                renderMembers: false,
-                ct: ct
-            ),
-            Token: tokenStr,
-            ExpiresAt: token.ExpiresAt
-        );
+        return Ok(await authService.GenerateUserTokenAsync(user));
     }
 
     private void CheckRequirements()

Foxnouns.Backend/Controllers/Authentication/EmailAuthController.cs

@@ -3,6 +3,7 @@ using Foxnouns.Backend.Database.Models;
 using Foxnouns.Backend.Extensions;
 using Foxnouns.Backend.Middleware;
 using Foxnouns.Backend.Services;
+using Foxnouns.Backend.Services.Auth;
 using Foxnouns.Backend.Utils;
 using JetBrains.Annotations;
 using Microsoft.AspNetCore.Mvc;
@@ -84,7 +85,7 @@ public class EmailAuthController(
         await keyCacheService.SetKeyAsync($"email:{ticket}", state.Email, Duration.FromMinutes(20));
 
         return Ok(
-            new AuthController.CallbackResponse(
+            new CallbackResponse(
                 HasAccount: false,
                 Ticket: ticket,
                 RemoteUsername: state.Email,

Foxnouns.Backend/Controllers/Authentication/FediverseAuthController.cs

@@ -1,11 +1,26 @@
+using Foxnouns.Backend.Database;
+using Foxnouns.Backend.Database.Models;
 using Foxnouns.Backend.Services;
+using Foxnouns.Backend.Services.Auth;
+using Foxnouns.Backend.Utils;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.EntityFrameworkCore;
+using NodaTime;
+using FediverseAuthService = Foxnouns.Backend.Services.Auth.FediverseAuthService;
 
 namespace Foxnouns.Backend.Controllers.Authentication;
 
 [Route("/api/internal/auth/fediverse")]
-public class FediverseAuthController(FediverseAuthService fediverseAuthService) : ApiControllerBase
+public class FediverseAuthController(
+    ILogger logger,
+    DatabaseContext db,
+    FediverseAuthService fediverseAuthService,
+    AuthService authService,
+    KeyCacheService keyCacheService
+) : ApiControllerBase
 {
+    private readonly ILogger _logger = logger.ForContext<FediverseAuthController>();
+
     [HttpGet]
     [ProducesResponseType<FediverseUrlResponse>(statusCode: StatusCodes.Status200OK)]
     public async Task<IActionResult> GetFediverseUrlAsync([FromQuery] string instance)
@@ -14,12 +29,88 @@ public class FediverseAuthController(FediverseAuthService fediverseAuthService)
         return Ok(new FediverseUrlResponse(url));
     }
 
+    [HttpPost("callback")]
+    [ProducesResponseType<CallbackResponse>(statusCode: StatusCodes.Status200OK)]
     public async Task<IActionResult> FediverseCallbackAsync([FromBody] CallbackRequest req)
     {
-        throw new NotImplementedException();
+        var app = await fediverseAuthService.GetApplicationAsync(req.Instance);
+        var remoteUser = await fediverseAuthService.GetRemoteFediverseUserAsync(app, req.Code);
+
+        var user = await authService.AuthenticateUserAsync(
+            AuthType.Fediverse,
+            remoteUser.Id,
+            instance: app
+        );
+        if (user != null)
+            return Ok(await authService.GenerateUserTokenAsync(user));
+
+        var ticket = AuthUtils.RandomToken();
+        await keyCacheService.SetKeyAsync(
+            $"fediverse:{ticket}",
+            new FediverseTicketData(app.Id, remoteUser),
+            Duration.FromMinutes(20)
+        );
+
+        return Ok(
+            new CallbackResponse(
+                HasAccount: false,
+                Ticket: ticket,
+                RemoteUsername: $"@{remoteUser.Username}@{app.Domain}",
+                User: null,
+                Token: null,
+                ExpiresAt: null
+            )
+        );
+    }
+
+    [HttpPost("register")]
+    [ProducesResponseType<AuthController.AuthResponse>(statusCode: StatusCodes.Status200OK)]
+    public async Task<IActionResult> RegisterAsync(
+        [FromBody] AuthController.OauthRegisterRequest req
+    )
+    {
+        var ticketData = await keyCacheService.GetKeyAsync<FediverseTicketData>(
+            $"fediverse:{req.Ticket}"
+        );
+        if (ticketData == null)
+            throw new ApiError.BadRequest("Invalid ticket", "ticket", req.Ticket);
+
+        var app = await db.FediverseApplications.FindAsync(ticketData.ApplicationId);
+        if (
+            await db.AuthMethods.AnyAsync(a =>
+                a.AuthType == AuthType.Fediverse
+                && a.RemoteId == ticketData.User.Id
+                && a.FediverseApplicationId == app.Id
+            )
+        )
+        {
+            _logger.Error(
+                "Fediverse user {Id}/{ApplicationId} ({Username} on {Domain}) has valid ticket but is already linked to an existing account",
+                ticketData.User.Id,
+                ticketData.ApplicationId,
+                ticketData.User.Username,
+                app.Domain
+            );
+            throw new ApiError.BadRequest("Invalid ticket", "ticket", req.Ticket);
+        }
+
+        var user = await authService.CreateUserWithRemoteAuthAsync(
+            req.Username,
+            AuthType.Fediverse,
+            ticketData.User.Id,
+            ticketData.User.Username,
+            instance: app
+        );
+
+        return Ok(await authService.GenerateUserTokenAsync(user));
     }
 
     public record CallbackRequest(string Instance, string Code);
 
     private record FediverseUrlResponse(string Url);
+
+    private record FediverseTicketData(
+        Snowflake ApplicationId,
+        FediverseAuthService.FediverseUser User
+    );
 }

Foxnouns.Backend/Extensions/WebApplicationExtensions.cs

@@ -4,12 +4,14 @@ using Foxnouns.Backend.Database;
 using Foxnouns.Backend.Jobs;
 using Foxnouns.Backend.Middleware;
 using Foxnouns.Backend.Services;
+using Foxnouns.Backend.Services.Auth;
 using Microsoft.EntityFrameworkCore;
 using Minio;
 using NodaTime;
 using Prometheus;
 using Serilog;
 using Serilog.Events;
+using FediverseAuthService = Foxnouns.Backend.Services.Auth.FediverseAuthService;
 using IClock = NodaTime.IClock;
 
 namespace Foxnouns.Backend.Extensions;

Foxnouns.Backend/Services/Auth/AuthService.cs

@@ -1,4 +1,5 @@
 using System.Security.Cryptography;
+using Foxnouns.Backend.Controllers.Authentication;
 using Foxnouns.Backend.Database;
 using Foxnouns.Backend.Database.Models;
 using Foxnouns.Backend.Utils;
@@ -6,10 +7,17 @@ using Microsoft.AspNetCore.Identity;
 using Microsoft.EntityFrameworkCore;
 using NodaTime;
 
-namespace Foxnouns.Backend.Services;
+namespace Foxnouns.Backend.Services.Auth;
 
-public class AuthService(IClock clock, DatabaseContext db, ISnowflakeGenerator snowflakeGenerator)
+public class AuthService(
+    IClock clock,
+    ILogger logger,
+    DatabaseContext db,
+    ISnowflakeGenerator snowflakeGenerator,
+    UserRendererService userRenderer
+)
 {
+    private readonly ILogger _logger = logger.ForContext<AuthService>();
     private readonly PasswordHasher<User> _passwordHasher = new();
 
     /// <summary>
@@ -256,6 +264,45 @@ public class AuthService(IClock clock, DatabaseContext db, ISnowflakeGenerator s
         );
     }
 
+    /// <summary>
+    /// Generates a token for the given user and adds it to the database, returning a fully formed auth response for the user.
+    /// This method is always called at the end of an endpoint method, so the resulting token
+    /// (and user, if this is a registration request) is also saved to the database.
+    /// </summary>
+    public async Task<CallbackResponse> GenerateUserTokenAsync(
+        User user,
+        CancellationToken ct = default
+    )
+    {
+        var frontendApp = await db.GetFrontendApplicationAsync(ct);
+
+        var (tokenStr, token) = GenerateToken(
+            user,
+            frontendApp,
+            ["*"],
+            clock.GetCurrentInstant() + Duration.FromDays(365)
+        );
+        db.Add(token);
+
+        _logger.Debug("Generated token {TokenId} for {UserId}", user.Id, token.Id);
+
+        await db.SaveChangesAsync(ct);
+
+        return new CallbackResponse(
+            HasAccount: true,
+            Ticket: null,
+            RemoteUsername: null,
+            User: await userRenderer.RenderUserAsync(
+                user,
+                selfUser: user,
+                renderMembers: false,
+                ct: ct
+            ),
+            Token: tokenStr,
+            ExpiresAt: token.ExpiresAt
+        );
+    }
+
     private static (string, byte[]) GenerateToken()
     {
         var token = AuthUtils.RandomToken();

Foxnouns.Backend/Services/Auth/FediverseAuthService.Mastodon.cs

@@ -5,12 +5,12 @@ using Foxnouns.Backend.Database.Models;
 using Duration = NodaTime.Duration;
 using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
 
-namespace Foxnouns.Backend.Services;
+namespace Foxnouns.Backend.Services.Auth;
 
 public partial class FediverseAuthService
 {
     private string MastodonRedirectUri(string instance) =>
-        $"{_config.BaseUrl}/auth/login/mastodon/{instance}";
+        $"{_config.BaseUrl}/auth/callback/mastodon/{instance}";
 
     private async Task<FediverseApplication> CreateMastodonApplicationAsync(
         string instance,

Foxnouns.Backend/Services/Auth/FediverseAuthService.cs

@@ -4,7 +4,7 @@ using Microsoft.EntityFrameworkCore;
 using NodaTime;
 using J = System.Text.Json.Serialization.JsonPropertyNameAttribute;
 
-namespace Foxnouns.Backend.Services;
+namespace Foxnouns.Backend.Services.Auth;
 
 public partial class FediverseAuthService
 {
@@ -43,12 +43,6 @@ public partial class FediverseAuthService
         return await GenerateAuthUrlAsync(app);
     }
 
-    public async Task<FediverseUser> GetRemoteFediverseUserAsync(string instance, string code)
-    {
-        var app = await GetApplicationAsync(instance);
-        return await GetRemoteUserAsync(app, code);
-    }
-
     // thank you, gargron and syuilo, for agreeing on a name for *once* in your lives,
     // and having both mastodon and misskey use "username" in the self user response
     public record FediverseUser(
@@ -56,7 +50,7 @@ public partial class FediverseAuthService
         [property: J("username")] string Username
     );
 
-    private async Task<FediverseApplication> GetApplicationAsync(string instance)
+    public async Task<FediverseApplication> GetApplicationAsync(string instance)
     {
         var app = await _db.FediverseApplications.FirstOrDefaultAsync(a => a.Domain == instance);
         if (app != null)
@@ -110,7 +104,10 @@ public partial class FediverseAuthService
             _ => throw new ArgumentOutOfRangeException(nameof(app), app.InstanceType, null),
         };
 
-    private async Task<FediverseUser> GetRemoteUserAsync(FediverseApplication app, string code) =>
+    public async Task<FediverseUser> GetRemoteFediverseUserAsync(
+        FediverseApplication app,
+        string code
+    ) =>
         app.InstanceType switch
         {
             FediverseInstanceType.MastodonApi => await GetMastodonUserAsync(app, code),

Foxnouns.Backend/Services/UserRendererService.cs

@@ -97,7 +97,7 @@ public class UserRendererService(
             ? $"{config.MediaBaseUrl}/users/{user.Id}/avatars/{user.Avatar}.webp"
             : null;
 
-    public string ImageUrlFor(PrideFlag flag) => $"{config.MediaBaseUrl}/flags/{flag.Hash}.webp";
+    private string ImageUrlFor(PrideFlag flag) => $"{config.MediaBaseUrl}/flags/{flag.Hash}.webp";
 
     public record UserResponse(
         Snowflake Id,

Foxnouns.Frontend/app/components/RegisterError.tsx

@@ -0,0 +1,36 @@
+import { ApiError, firstErrorFor } from "~/lib/api/error";
+import { Trans, useTranslation } from "react-i18next";
+import { Alert } from "react-bootstrap";
+import { Link } from "@remix-run/react";
+import ErrorAlert from "~/components/ErrorAlert";
+
+export default function RegisterError({ error }: { error: ApiError }) {
+	const { t } = useTranslation();
+
+	// TODO: maybe turn these messages into their own error codes?
+	const ticketMessage = firstErrorFor(error, "ticket")?.message;
+	const usernameMessage = firstErrorFor(error, "username")?.message;
+
+	if (ticketMessage === "Invalid ticket") {
+		return (
+			<Alert variant="danger">
+				<Alert.Heading as="h4">{t("error.heading")}</Alert.Heading>
+				<Trans t={t} i18nKey={"log-in.callback.invalid-ticket"}>
+					Invalid ticket (it might have been too long since you logged in), please{" "}
+					<Link to="/auth/log-in">try again</Link>.
+				</Trans>
+			</Alert>
+		);
+	}
+
+	if (usernameMessage === "Username is already taken") {
+		return (
+			<Alert variant="danger">
+				<Alert.Heading as="h4">{t("log-in.callback.invalid-username")}</Alert.Heading>
+				{t("log-in.callback.username-taken")}
+			</Alert>
+		);
+	}
+
+	return <ErrorAlert error={error} />;
+}

Foxnouns.Frontend/app/lib/request.server.ts

@@ -30,7 +30,7 @@ export async function baseRequest(
 		headers: {
 			...params.headers,
 			...(params.token ? { Authorization: params.token } : {}),
-			"Content-Type": "application/json",
+			...(params.body ? { "Content-Type": "application/json" } : {}),
 		},
 	});
 

Foxnouns.Frontend/app/routes/auth.callback.discord/route.tsx

@@ -22,6 +22,7 @@ import ErrorAlert from "~/components/ErrorAlert";
 import i18n from "~/i18next.server";
 import { tokenCookieName } from "~/lib/utils";
 import { useEffect } from "react";
+import RegisterError from "~/components/RegisterError";
 
 export const meta: MetaFunction<typeof loader> = ({ data }) => {
 	return [{ title: `${data?.meta.title || "Log in"} • pronouns.cc` }];
@@ -163,34 +164,3 @@ export default function DiscordCallbackPage() {
 		</RemixForm>
 	);
 }
-
-function RegisterError({ error }: { error: ApiError }) {
-	const { t } = useTranslation();
-
-	// TODO: maybe turn these messages into their own error codes?
-	const ticketMessage = firstErrorFor(error, "ticket")?.message;
-	const usernameMessage = firstErrorFor(error, "username")?.message;
-
-	if (ticketMessage === "Invalid ticket") {
-		return (
-			<Alert variant="danger">
-				<Alert.Heading as="h4">{t("error.heading")}</Alert.Heading>
-				<Trans t={t} i18nKey={"log-in.callback.invalid-ticket"}>
-					Invalid ticket (it might have been too long since you logged in with Discord), please{" "}
-					<Link to="/auth/log-in">try again</Link>.
-				</Trans>
-			</Alert>
-		);
-	}
-
-	if (usernameMessage === "Username is already taken") {
-		return (
-			<Alert variant="danger">
-				<Alert.Heading as="h4">{t("log-in.callback.invalid-username")}</Alert.Heading>
-				{t("log-in.callback.username-taken")}
-			</Alert>
-		);
-	}
-
-	return <ErrorAlert error={error} />;
-}

Foxnouns.Frontend/app/routes/auth.callback.mastodon.$instance/route.tsx

@@ -0,0 +1,163 @@
+import {
+	ActionFunctionArgs,
+	json,
+	LoaderFunctionArgs,
+	MetaFunction,
+	redirect,
+} from "@remix-run/node";
+import i18n from "~/i18next.server";
+import { type ApiError, ErrorCode } from "~/lib/api/error";
+import serverRequest, { writeCookie } from "~/lib/request.server";
+import { AuthResponse, CallbackResponse } from "~/lib/api/auth";
+import { tokenCookieName } from "~/lib/utils";
+import {
+	Link,
+	ShouldRevalidateFunction,
+	useActionData,
+	useLoaderData,
+	useNavigate,
+} from "@remix-run/react";
+import { Trans, useTranslation } from "react-i18next";
+import { useEffect } from "react";
+import { Form as RemixForm } from "@remix-run/react/dist/components";
+import { Button, Form } from "react-bootstrap";
+import RegisterError from "~/components/RegisterError";
+
+export const meta: MetaFunction<typeof loader> = ({ data }) => {
+	return [{ title: `${data?.meta.title || "Log in"} • pronouns.cc` }];
+};
+
+export const shouldRevalidate: ShouldRevalidateFunction = ({ actionResult }) => {
+	return !actionResult;
+};
+
+export const loader = async ({ request, params }: LoaderFunctionArgs) => {
+	const t = await i18n.getFixedT(request);
+	const url = new URL(request.url);
+
+	const code = url.searchParams.get("code");
+	if (!code) throw { status: 400, code: ErrorCode.BadRequest, message: "Missing code" } as ApiError;
+
+	const resp = await serverRequest<CallbackResponse>("POST", "/auth/fediverse/callback", {
+		body: { code, instance: params.instance! },
+		isInternal: true,
+	});
+
+	if (resp.has_account) {
+		return json(
+			{
+				meta: { title: t("log-in.callback.title.fediverse-success") },
+				hasAccount: true,
+				user: resp.user!,
+				ticket: null,
+				remoteUser: null,
+			},
+			{
+				headers: {
+					"Set-Cookie": writeCookie(tokenCookieName, resp.token!),
+				},
+			},
+		);
+	}
+
+	return json({
+		meta: { title: t("log-in.callback.title.fediverse-register") },
+		hasAccount: false,
+		user: null,
+		instance: params.instance!,
+		ticket: resp.ticket!,
+		remoteUser: resp.remote_username!,
+	});
+};
+
+export const action = async ({ request }: ActionFunctionArgs) => {
+	const data = await request.formData();
+	const username = data.get("username") as string | null;
+	const ticket = data.get("ticket") as string | null;
+
+	if (!username || !ticket)
+		return json({
+			error: {
+				status: 403,
+				code: ErrorCode.BadRequest,
+				message: "Invalid username or ticket",
+			} as ApiError,
+			user: null,
+		});
+
+	try {
+		const resp = await serverRequest<AuthResponse>("POST", "/auth/fediverse/register", {
+			body: { username, ticket },
+			isInternal: true,
+		});
+
+		return redirect("/auth/welcome", {
+			headers: {
+				"Set-Cookie": writeCookie(tokenCookieName, resp.token),
+			},
+			status: 303,
+		});
+	} catch (e) {
+		JSON.stringify(e);
+
+		return json({ error: e as ApiError });
+	}
+};
+
+export default function FediverseCallbackPage() {
+	const { t } = useTranslation();
+	const data = useLoaderData<typeof loader>();
+	const actionData = useActionData<typeof action>();
+	const navigate = useNavigate();
+
+	useEffect(() => {
+		setTimeout(() => {
+			if (data.hasAccount) {
+				navigate(`/@${data.user!.username}`);
+			}
+		}, 2000);
+		// eslint-disable-next-line react-hooks/exhaustive-deps
+	}, []);
+
+	if (data.hasAccount) {
+		const username = data.user!.username;
+
+		return (
+			<>
+				<h1>{t("log-in.callback.success")}</h1>
+				<p>
+					<Trans
+						t={t}
+						i18nKey={"log-in.callback.success-link"}
+						values={{ username: data.user!.username }}
+					>
+						{/* @ts-expect-error react-i18next handles interpolation here */}
+						Welcome back, <Link to={`/@${data.user!.username}`}>@{{ username }}</Link>!
+					</Trans>
+					<br />
+					{t("log-in.callback.redirect-hint")}
+				</p>
+			</>
+		);
+	}
+
+	return (
+		<RemixForm method="POST">
+			<Form as="div">
+				{actionData?.error && <RegisterError error={actionData.error} />}
+				<Form.Group className="mb-3" controlId="remote-username">
+					<Form.Label>{t("log-in.callback.remote-username.fediverse")}</Form.Label>
+					<Form.Control type="text" readOnly={true} value={data.remoteUser!} />
+				</Form.Group>
+				<Form.Group className="mb-3" controlId="username">
+					<Form.Label>{t("log-in.callback.username")}</Form.Label>
+					<Form.Control name="username" type="text" required />
+				</Form.Group>
+				<input type="hidden" name="ticket" value={data.ticket!} />
+				<Button variant="primary" type="submit">
+					{t("log-in.callback.sign-up-button")}
+				</Button>
+			</Form>
+		</RemixForm>
+	);
+}

Foxnouns.Frontend/app/routes/auth.log-in/route.tsx

@@ -126,6 +126,9 @@ export default function LoginPage() {
 								{t("log-in.3rd-party.tumblr")}
 							</ListGroup.Item>
 						)}
+						<ListGroup.Item action href="/auth/log-in/fediverse">
+							{t("log-in.3rd-party.fediverse")}
+						</ListGroup.Item>
 					</ListGroup>
 				</div>
 				{!urls.email_enabled && <div className="col-lg-3"></div>}

Foxnouns.Frontend/app/routes/auth.log-in_.fediverse/route.tsx

@@ -0,0 +1,75 @@
+import {
+	LoaderFunctionArgs,
+	json,
+	MetaFunction,
+	ActionFunctionArgs,
+	redirect,
+} from "@remix-run/node";
+import i18n from "~/i18next.server";
+import { useTranslation } from "react-i18next";
+import { Form as RemixForm, useActionData } from "@remix-run/react";
+import { Button, Form } from "react-bootstrap";
+import serverRequest from "~/lib/request.server";
+import { ApiError, ErrorCode } from "~/lib/api/error";
+import ErrorAlert from "~/components/ErrorAlert";
+
+export const meta: MetaFunction<typeof loader> = ({ data }) => {
+	return [{ title: `${data?.meta.title || "Log in with a Fediverse account"} • pronouns.cc` }];
+};
+
+export const loader = async ({ request }: LoaderFunctionArgs) => {
+	const t = await i18n.getFixedT(request);
+
+	return json({ meta: { title: t("log-in.fediverse.choose-title") } });
+};
+
+export const action = async ({ request }: ActionFunctionArgs) => {
+	const body = await request.formData();
+	const instance = body.get("instance") as string | null;
+	if (!instance)
+		return json({
+			error: {
+				status: 403,
+				code: ErrorCode.BadRequest,
+				message: "Invalid instance name",
+			} as ApiError,
+		});
+
+	try {
+		const resp = await serverRequest<{ url: string }>(
+			"GET",
+			`/auth/fediverse?instance=${encodeURIComponent(instance)}`,
+			{
+				isInternal: true,
+			},
+		);
+
+		return redirect(resp.url);
+	} catch (e) {
+		return json({ error: e as ApiError });
+	}
+};
+
+export default function AuthFediversePage() {
+	const { t } = useTranslation();
+
+	const data = useActionData<typeof action>();
+
+	return (
+		<>
+			<h2>{t("log-in.fediverse.choose-form-title")}</h2>
+			{data?.error && <ErrorAlert error={data.error} />}
+			<RemixForm method="POST">
+				<Form as="div">
+					<Form.Group className="mb-3" controlId="instance">
+						<Form.Label>{t("log-in.fediverse-instance-label")}</Form.Label>
+						<Form.Control name="instance" type="text" />
+					</Form.Group>
+					<Button variant="primary" type="submit">
+						{t("log-in.fediverse-log-in-button")}
+					</Button>
+				</Form>
+			</RemixForm>
+		</>
+	);
+}

Foxnouns.Frontend/public/locales/en.json

@@ -47,22 +47,31 @@
 	},
 	"log-in": {
 		"callback": {
+			"invalid-ticket": "Invalid ticket (it might have been too long since you logged in), please <2>try again</2>.",
+			"invalid-username": "Invalid username",
+			"username-taken": "That username is already taken, please try something else.",
 			"title": {
 				"discord-success": "Log in with Discord",
-				"discord-register": "Register with Discord"
+				"discord-register": "Register with Discord",
+				"fediverse-success": "Log in with a Fediverse account",
+				"fediverse-register": "Register with a Fediverse account"
 			},
 			"success": "Successfully logged in!",
 			"success-link": "Welcome back, <1>@{{username}}</1>!",
 			"redirect-hint": "If you're not redirected to your profile in a few seconds, press the link above.",
 			"remote-username": {
-				"discord": "Your discord username"
+				"discord": "Your Discord username",
+				"fediverse": "Your Fediverse account"
 			},
 			"username": "Username",
-			"sign-up-button": "Sign up",
-			"invalid-ticket": "Invalid ticket (it might have been too long since you logged in with Discord), please <2>try again</2>.",
-			"invalid-username": "Invalid username",
-			"username-taken": "That username is already taken, please try something else."
+			"sign-up-button": "Sign up"
 		},
+		"fediverse": {
+			"choose-title": "Log in with a Fediverse account",
+			"choose-form-title": "Choose a Fediverse instance"
+		},
+		"fediverse-instance-label": "Your Fediverse instance",
+		"fediverse-log-in-button": "Log in",
 		"title": "Log in",
 		"form-title": "Log in with email",
 		"email": "Email address",
@@ -74,7 +83,8 @@
 			"desc": "If you prefer, you can also log in with one of these services:",
 			"discord": "Log in with Discord",
 			"google": "Log in with Google",
-			"tumblr": "Log in with Tumblr"
+			"tumblr": "Log in with Tumblr",
+			"fediverse": "Log in with the Fediverse"
 		},
 		"invalid-credentials": "Invalid email address or password, please check your spelling and try again."
 	},