Auth endpoint

The IndieAuth endpoint should be added, currently adding the unt tests

app/Http/Controllers/Admin/PasskeysController.php

@@ -19,7 +19,6 @@ use Illuminate\Support\Facades\Auth;
 use Illuminate\View\View;
 use ParagonIE\ConstantTime\Base64UrlSafe;
 use Throwable;
-use Webauthn\AttestationStatement\AttestationObjectLoader;
 use Webauthn\AttestationStatement\AttestationStatementSupportManager;
 use Webauthn\AttestationStatement\NoneAttestationStatementSupport;
 use Webauthn\AuthenticationExtensions\ExtensionOutputCheckerHandler;
@@ -28,9 +27,11 @@ use Webauthn\AuthenticatorAssertionResponseValidator;
 use Webauthn\AuthenticatorAttestationResponse;
 use Webauthn\AuthenticatorAttestationResponseValidator;
 use Webauthn\AuthenticatorSelectionCriteria;
+use Webauthn\CeremonyStep\CeremonyStepManagerFactory;
+use Webauthn\Denormalizer\WebauthnSerializerFactory;
 use Webauthn\Exception\WebauthnException;
+use Webauthn\PublicKeyCredential;
 use Webauthn\PublicKeyCredentialCreationOptions;
-use Webauthn\PublicKeyCredentialLoader;
 use Webauthn\PublicKeyCredentialParameters;
 use Webauthn\PublicKeyCredentialRequestOptions;
 use Webauthn\PublicKeyCredentialRpEntity;
@@ -109,39 +110,57 @@ class PasskeysController extends Controller
         $user = auth()->user();
 
         $publicKeyCredentialCreationOptionsData = session('create_options');
+        // Unset session data to mitigate replay attacks
+        session()->forget('create_options');
         if (empty($publicKeyCredentialCreationOptionsData)) {
             throw new WebAuthnException('No public key credential request options found');
         }
-        $publicKeyCredentialCreationOptions = PublicKeyCredentialCreationOptions::createFromString($publicKeyCredentialCreationOptionsData);
 
-        // Unset session data to mitigate replay attacks
-        session()->forget('create_options');
+        $attestationStatementSupportManager = new AttestationStatementSupportManager();
+        $attestationStatementSupportManager->add(new NoneAttestationStatementSupport());
 
-        $attestationSupportManager = AttestationStatementSupportManager::create();
-        $attestationSupportManager->add(NoneAttestationStatementSupport::create());
-        $attestationObjectLoader = AttestationObjectLoader::create($attestationSupportManager);
-        $publicKeyCredentialLoader = PublicKeyCredentialLoader::create($attestationObjectLoader);
+        $webauthnSerializer = (new WebauthnSerializerFactory(
+            $attestationStatementSupportManager
+        ))->create();
 
-        $publicKeyCredential = $publicKeyCredentialLoader->load(json_encode($request->all(), JSON_THROW_ON_ERROR));
+        $publicKeyCredential = $webauthnSerializer->deserialize(
+            json_encode($request->all(), JSON_THROW_ON_ERROR),
+            PublicKeyCredential::class,
+            'json'
+        );
 
         if (! $publicKeyCredential->response instanceof AuthenticatorAttestationResponse) {
             throw new WebAuthnException('Invalid response type');
         }
 
-        $attestationStatementSupportManager = AttestationStatementSupportManager::create();
-        $attestationStatementSupportManager->add(NoneAttestationStatementSupport::create());
+        $algorithmManager = new Manager();
+        $algorithmManager->add(new Ed25519());
+        $algorithmManager->add(new ES256());
+        $algorithmManager->add(new RS256());
 
-        $authenticatorAttestationResponseValidator = AuthenticatorAttestationResponseValidator::create(
-            attestationStatementSupportManager: $attestationStatementSupportManager,
-            publicKeyCredentialSourceRepository: null,
-            tokenBindingHandler: null,
-            extensionOutputCheckerHandler: ExtensionOutputCheckerHandler::create(),
+        $ceremonyStepManagerFactory = new CeremonyStepManagerFactory();
+        $ceremonyStepManagerFactory->setAlgorithmManager($algorithmManager);
+        $ceremonyStepManagerFactory->setAttestationStatementSupportManager(
+            $attestationStatementSupportManager
+        );
+        $ceremonyStepManagerFactory->setExtensionOutputCheckerHandler(
+            ExtensionOutputCheckerHandler::create()
         );
-
         $securedRelyingPartyId = [];
         if (App::environment('local', 'development')) {
             $securedRelyingPartyId = [config('url.longurl')];
         }
+        $ceremonyStepManagerFactory->setSecuredRelyingPartyId($securedRelyingPartyId);
+
+        $authenticatorAttestationResponseValidator = AuthenticatorAttestationResponseValidator::create(
+            ceremonyStepManager: $ceremonyStepManagerFactory->creationCeremony()
+        );
+
+        $publicKeyCredentialCreationOptions = $webauthnSerializer->deserialize(
+            $publicKeyCredentialCreationOptionsData,
+            PublicKeyCredentialCreationOptions::class,
+            'json'
+        );
 
         $publicKeyCredentialSource = $authenticatorAttestationResponseValidator->check(
             authenticatorAttestationResponse: $publicKeyCredential->response,
@@ -187,14 +206,18 @@ class PasskeysController extends Controller
             ], 400);
         }
 
-        $publicKeyCredentialRequestOptions = PublicKeyCredentialRequestOptions::createFromString($requestOptions);
+        $attestationStatementSupportManager = new AttestationStatementSupportManager();
+        $attestationStatementSupportManager->add(new NoneAttestationStatementSupport());
 
-        $attestationSupportManager = AttestationStatementSupportManager::create();
-        $attestationSupportManager->add(NoneAttestationStatementSupport::create());
-        $attestationObjectLoader = AttestationObjectLoader::create($attestationSupportManager);
-        $publicKeyCredentialLoader = PublicKeyCredentialLoader::create($attestationObjectLoader);
+        $webauthnSerializer = (new WebauthnSerializerFactory(
+            $attestationStatementSupportManager
+        ))->create();
 
-        $publicKeyCredential = $publicKeyCredentialLoader->load(json_encode($request->all(), JSON_THROW_ON_ERROR));
+        $publicKeyCredential = $webauthnSerializer->deserialize(
+            json_encode($request->all(), JSON_THROW_ON_ERROR),
+            PublicKeyCredential::class,
+            'json'
+        );
 
         if (! $publicKeyCredential->response instanceof AuthenticatorAssertionResponse) {
             return response()->json([
@@ -211,28 +234,47 @@ class PasskeysController extends Controller
             ], 404);
         }
 
-        $credential = PublicKeyCredentialSource::createFromArray(json_decode($passkey->passkey, true, 512, JSON_THROW_ON_ERROR));
+        $publicKeyCredentialSource = $webauthnSerializer->deserialize(
+            $passkey->passkey,
+            PublicKeyCredentialSource::class,
+            'json'
+        );
 
-        $algorithmManager = Manager::create();
+        $algorithmManager = new Manager();
         $algorithmManager->add(new Ed25519());
         $algorithmManager->add(new ES256());
         $algorithmManager->add(new RS256());
 
-        $authenticatorAssertionResponseValidator = new AuthenticatorAssertionResponseValidator(
-            publicKeyCredentialSourceRepository: null,
-            tokenBindingHandler: null,
-            extensionOutputCheckerHandler: ExtensionOutputCheckerHandler::create(),
-            algorithmManager: $algorithmManager,
-        );
+        $attestationStatementSupportManager = new AttestationStatementSupportManager();
+        $attestationStatementSupportManager->add(new NoneAttestationStatementSupport());
 
+        $ceremonyStepManagerFactory = new CeremonyStepManagerFactory();
+        $ceremonyStepManagerFactory->setAlgorithmManager($algorithmManager);
+        $ceremonyStepManagerFactory->setAttestationStatementSupportManager(
+            $attestationStatementSupportManager
+        );
+        $ceremonyStepManagerFactory->setExtensionOutputCheckerHandler(
+            ExtensionOutputCheckerHandler::create()
+        );
         $securedRelyingPartyId = [];
         if (App::environment('local', 'development')) {
             $securedRelyingPartyId = [config('url.longurl')];
         }
+        $ceremonyStepManagerFactory->setSecuredRelyingPartyId($securedRelyingPartyId);
+
+        $authenticatorAssertionResponseValidator = AuthenticatorAssertionResponseValidator::create(
+            ceremonyStepManager: $ceremonyStepManagerFactory->requestCeremony()
+        );
+
+        $publicKeyCredentialRequestOptions = $webauthnSerializer->deserialize(
+            $requestOptions,
+            PublicKeyCredentialRequestOptions::class,
+            'json'
+        );
 
         try {
             $authenticatorAssertionResponseValidator->check(
-                credentialId: $credential,
+                credentialId: $publicKeyCredentialSource,
                 authenticatorAssertionResponse: $publicKeyCredential->response,
                 publicKeyCredentialRequestOptions: $publicKeyCredentialRequestOptions,
                 request: config('url.longurl'),

app/Http/Controllers/IndieAuthController.php

@@ -0,0 +1,202 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Http\Controllers;
+
+use Exception;
+use GuzzleHttp\Client;
+use GuzzleHttp\Psr7\Uri;
+use Illuminate\Http\JsonResponse;
+use Illuminate\Http\Request;
+use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\Validator;
+use Illuminate\View\View;
+use Random\RandomException;
+use SodiumException;
+
+class IndieAuthController extends Controller
+{
+    /**
+     * Process a GET request to the IndieAuth endpoint.
+     *
+     * This is the first step in the IndieAuth flow, where the client app sends the user to the IndieAuth endpoint.
+     */
+    public function start(Request $request): View
+    {
+        // First check all required params are present
+        $validator = Validator::make($request->all(), [
+            'response_type' => 'required:string',
+            'client_id' => 'required',
+            'redirect_uri' => 'required',
+            'state' => 'required',
+            'code_challenge' => 'required:string',
+            'code_challenge_method' => 'required:string',
+        ], [
+            'response_type' => 'response_type is required',
+            'client_id.required' => 'client_id is required to display which app is asking for authentication',
+            'redirect_uri.required' => 'redirect_uri is required so we can progress successful requests',
+            'state.required' => 'state is required',
+            'code_challenge.required' => 'code_challenge is required',
+            'code_challenge_method.required' => 'code_challenge_method is required',
+        ]);
+
+        if ($validator->fails()) {
+            return view('indieauth.error')->withErrors($validator);
+        }
+
+        if ($request->get('response_type') !== 'code') {
+            return view('indieauth.error')->withErrors(['response_type' => 'only a response_type of "code" is supported']);
+        }
+
+        if (mb_strtoupper($request->get('code_challenge_method')) !== 'S256') {
+            return view('indieauth.error')->withErrors(['code_challenge_method' => 'only a code_challenge_method of "S256" is supported']);
+        }
+
+        if (! $this->isValidRedirectUri($request->get('client_id'), $request->get('redirect_uri'))) {
+            return view('indieauth.error')->withErrors(['redirect_uri' => 'redirect_uri is not valid for this client_id']);
+        }
+
+        $scopes = $request->get('scopes', '');
+        $scopes = explode(' ', $scopes);
+
+        return view('indieauth.start', [
+            'me' => $request->get('me'),
+            'client_id' => $request->get('client_id'),
+            'redirect_uri' => $request->get('redirect_uri'),
+            'state' => $request->get('state'),
+            'scopes' => $scopes,
+            'code_challenge' => $request->get('code_challenge'),
+            'code_challenge_method' => $request->get('code_challenge_method'),
+        ]);
+    }
+
+    /**
+     * Confirm an IndieAuth approval request.
+     *
+     * Generates an auth code and redirects the user back to the client app.
+     *
+     * @throws RandomException
+     */
+    public function confirm(Request $request): JsonResponse
+    {
+        $authCode = bin2hex(random_bytes(16));
+
+        $cacheKey = hash('xxh3', $request->get('client_id'));
+
+        $indieAuthRequestData = [
+            'code_challenge' => $request->get('code_challenge'),
+            'code_challenge_method' => $request->get('code_challenge_method'),
+            'client_id' => $request->get('client_id'),
+            'auth_code' => $authCode,
+        ];
+
+        Cache::put($cacheKey, $indieAuthRequestData, now()->addMinutes(10));
+
+        $redirectUri = new Uri($request->get('redirect_uri'));
+        $redirectUri = Uri::withQueryValues($redirectUri, [
+            'code' => $authCode,
+            'me' => $request->get('me'),
+            'state' => $request->get('state'),
+        ]);
+
+        // For now just dump URL scheme
+        return response()->json([
+            'redirect_uri' => $redirectUri,
+        ]);
+    }
+
+    /**
+     * Process a POST request to the IndieAuth endpoint.
+     *
+     * This is the second step in the IndieAuth flow, where the client app sends the auth code to the IndieAuth endpoint.
+     * @throws SodiumException
+     */
+    public function processCodeExchange(Request $request): JsonResponse
+    {
+        // First check all the data is present
+        $validator = Validator::make($request->all(), [
+            'grant_type' => 'required:string',
+            'code' => 'required:string',
+            'client_id' => 'required',
+            'redirect_uri' => 'required',
+            'code_verifier' => 'required',
+        ]);
+
+        if ($validator->fails()) {
+            return response()->json($validator->errors(), 400);
+        }
+
+        if ($request->get('grant_type') !== 'authorization_code') {
+            return response()->json(['error' => 'only a grant_type of "authorization_code" is supported'], 400);
+        }
+
+        // Check cache for auth code
+        $cacheKey = hash('xxh3', $request->get('client_id'));
+        $indieAuthRequestData = Cache::pull($cacheKey);
+
+        if ($indieAuthRequestData === null) {
+            return response()->json(['error' => 'code is invalid'], 404);
+        }
+
+        if ($indieAuthRequestData['auth_code'] !== $request->get('code')) {
+            return response()->json(['error' => 'code is invalid'], 400);
+        }
+
+        // Check code verifier
+        if (! hash_equals(
+            $indieAuthRequestData['code_challenge'],
+            sodium_bin2base64(
+                hash('sha256', $request->get('code_verifier'), true),
+                SODIUM_BASE64_VARIANT_URLSAFE_NO_PADDING
+            )
+        )) {
+            return response()->json(['error' => 'code_verifier is invalid'], 400);
+        }
+
+        return response()->json([
+            'me' => config('app.url'),
+        ]);
+    }
+
+    protected function isValidRedirectUri(string $clientId, string $redirectUri): bool
+    {
+        // If client_id is not a valid URL, then it's not valid
+        $clientIdParsed = \Mf2\parseUriToComponents($clientId);
+        if (! isset($clientIdParsed['authority'])) {
+            ray($clientIdParsed);
+
+            return false;
+        }
+
+        // If redirect_uri is not a valid URL, then it's not valid
+        $redirectUriParsed = \Mf2\parseUriToComponents($redirectUri);
+        if (! isset($redirectUriParsed['authority'])) {
+            ray($redirectUriParsed);
+
+            return false;
+        }
+
+        // If client_id and redirect_uri are the same host, then it's valid
+        if ($clientIdParsed['authority'] === $redirectUriParsed['authority']) {
+            return true;
+        }
+
+        // Otherwise we need to check the redirect_uri is in the client_id's redirect_uris
+        $guzzle = resolve(Client::class);
+
+        try {
+            $clientInfo = $guzzle->get($clientId);
+        } catch (Exception $e) {
+            ray('Failed to fetch client info', $e->getMessage());
+
+            return false;
+        }
+
+        $clientInfoParsed = \Mf2\parse($clientInfo->getBody()->getContents(), $clientId);
+
+        $redirectUris = $clientInfoParsed['rels']['redirect_uri'] ?? [];
+
+        return in_array($redirectUri, $redirectUris);
+    }
+}

app/Http/Middleware/MyAuthMiddleware.php

@@ -20,6 +20,8 @@ class MyAuthMiddleware
     {
         if (Auth::check() === false) {
             // they’re not logged in, so send them to login form
+            redirect()->setIntendedUrl($request->url());
+
             return redirect()->route('login');
         }
 

composer.json

@@ -10,6 +10,7 @@
         "ext-intl": "*",
         "ext-json": "*",
         "ext-pgsql": "*",
+        "ext-sodium": "*",
         "cviebrock/eloquent-sluggable": "^11.0",
         "guzzlehttp/guzzle": "^7.2",
         "indieauth/client": "^1.1",
@@ -26,9 +27,12 @@
         "league/commonmark": "^2.0",
         "league/flysystem-aws-s3-v3": "^3.0",
         "mf2/mf2": "~0.3",
+        "phpdocumentor/reflection-docblock": "^5.3",
         "spatie/commonmark-highlighter": "^3.0",
         "spatie/laravel-ignition": "^2.1",
         "symfony/html-sanitizer": "^7.0",
+        "symfony/property-access": "^7.0",
+        "symfony/serializer": "^7.0",
         "web-auth/webauthn-lib": "^4.7"
     },
     "require-dev": {

docker-compose.yml

@@ -1,5 +1,4 @@
 # For more information: https://laravel.com/docs/sail
-version: '3'
 services:
     laravel.test:
         build:
@@ -18,6 +17,7 @@ services:
             LARAVEL_SAIL: 1
             XDEBUG_MODE: '${SAIL_XDEBUG_MODE:-off}'
             XDEBUG_CONFIG: '${SAIL_XDEBUG_CONFIG:-client_host=host.docker.internal}'
+            IGNITION_LOCAL_SITES_PATH: '${PWD}'
         volumes:
             - '.:/var/www/html'
         networks:

public/assets/css/app.css

@@ -5,3 +5,4 @@
 @import url('code.css');
 @import url('content.css');
 @import url('notes.css');
+@import url('indieauth.css');

public/assets/css/indieauth.css

@@ -0,0 +1,15 @@
+.indieauth {
+  .error {
+    color: var(--color-danger);
+    background-color: var(--color-danger-shadow);
+    border: 1px solid var(--color-danger);
+    border-radius: .5rem;
+
+    display: flex;
+    padding-inline: 1rem;
+    padding-block: .5rem;
+    width: fit-content;
+
+    margin-block-end: 1rem;
+  }
+}

public/assets/css/variables.css

@@ -20,4 +20,6 @@
   --color-link-visited: oklch(70.44% 0.21 304.41deg);
   --color-primary-shadow: oklch(19.56% 0.054 125.505deg / 40%);
   --rss-color-link: oklch(67.59% 0.189 42.04deg);
+  --color-danger: oklch(64.41% 0.281 23.29deg);
+  --color-danger-shadow: oklch(64.41% 0.281 23.29deg / 10%);
 }

resources/views/indieauth/error.blade.php

@@ -0,0 +1,12 @@
+@extends('master')
+
+@section('title')IndieAuth « @stop
+
+@section('content')
+    <section class="indieauth">
+        <h1>IndieAuth</h1>
+        @foreach ($errors->all() as $message)
+            <div class="error">{{ $message }}</div>
+        @endforeach
+    </section>
+@stop

resources/views/indieauth/start.blade.php

@@ -0,0 +1,39 @@
+@extends('master')
+
+@section('title')IndieAuth « @stop
+
+@section('content')
+    <form class="indieauth" action="/auth/confirm" method="post">
+        @csrf
+
+        <input type="hidden" name="client_id" value="{{ $client_id }}">
+        <input type="hidden" name="redirect_uri" value="{{ $redirect_uri }}">
+        <input type="hidden" name="state" value="{{ $state }}">
+        <input type="hidden" name="me" value="{{ $me }}">
+        <input type="hidden" name="code_challenge" value="{{ $code_challenge }}">
+        <input type="hidden" name="code_challenge_method" value="{{ $code_challenge_method }}">
+        @if(!empty($scopes))
+            @foreach($scopes as $scope)
+                <input type="hidden" name="scope[]" value="{{ $scope }}">
+            @endforeach
+        @endif
+
+        <h1>IndieAuth</h1>
+        @if(!empty($error))
+            <div class="error">{{ $error }}</div>
+        @endif
+
+        <p>You are attempting to log in with the client <code>{{ $client_id }}</code></p>
+        <p>After approving the request you will be redirected to <code>{{ $redirect_uri }}</code></p>
+        @if(!empty($scopes))
+            <p>The client is requesting the following scopes:</p>
+            <ul>
+                @foreach($scopes as $scope)
+                    <li>{{ $scope }}</li>
+                @endforeach
+            </ul>
+        @endif
+
+        <button type="submit">Approve</button>
+    </form>
+@stop

routes/web.php

@@ -16,6 +16,7 @@ use App\Http\Controllers\BookmarksController;
 use App\Http\Controllers\ContactsController;
 use App\Http\Controllers\FeedsController;
 use App\Http\Controllers\FrontPageController;
+use App\Http\Controllers\IndieAuthController;
 use App\Http\Controllers\LikesController;
 use App\Http\Controllers\MicropubController;
 use App\Http\Controllers\MicropubMediaController;
@@ -190,6 +191,23 @@ Route::domain(config('url.longurl'))->group(function () {
         Route::get('/tagged/{tag}', [BookmarksController::class, 'tagged']);
     });
 
+    // IndieAuth
+    Route::get('auth', [IndieAuthController::class, 'start'])->middleware(MyAuthMiddleware::class);
+    Route::post('auth/confirm', [IndieAuthController::class, 'confirm'])->middleware(MyAuthMiddleware::class);
+    Route::post('auth', [IndieAuthController::class, 'processCodeExchange']);
+
+    Route::get('/test-auth-cache', function () {
+        $cacheKey = hash('xxh3', 'http://jonnybarnes.localhost');
+
+        dump(Cache::get($cacheKey));
+    });
+
+    Route::get('/test-me', function () {
+        return response()->json([
+            'me' => config('app.url'),
+        ]);
+    });
+
     // Token Endpoint
     Route::post('api/token', [TokenEndpointController::class, 'create']);
 

tests/Feature/IndieAuthTest.php

@@ -0,0 +1,206 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Feature;
+
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use PHPUnit\Framework\Attributes\Test;
+use Tests\TestCase;
+
+class IndieAuthTest extends TestCase
+{
+    use RefreshDatabase;
+
+    #[Test]
+    public function itShouldReturnApprovalViewWhenTheRequestIsValid(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'code',
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+            'code_challenge_method' => 'S256',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.start');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenResponeTypeIsWrong(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'invalid_value',
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+            'code_challenge_method' => 'S256',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('only a response_type of "code" is supported');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenResponeTypeIsMissing(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+            'code_challenge_method' => 'S256',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('response_type is required');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenClientIdIsMissing(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'code',
+            'me' => 'https://example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+            'code_challenge_method' => 'S256',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('client_id is required');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenRedirectUriIsMissing(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'code',
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+            'code_challenge_method' => 'S256',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('redirect_uri is required');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenStateIsMissing(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'code',
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+            'code_challenge_method' => 'S256',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('state is required');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenCodeChallengeIsMissing(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'code',
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge_method' => 'S256',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('code_challenge is required');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenCodeChallengeMethodIsMissing(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'code',
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('code_challenge_method is required');
+    }
+
+    #[Test]
+    public function itShouldReturnErrorViewWhenCodeChallengeMethodIsUnsupportedValue(): void
+    {
+        $user = User::factory()->make();
+        $url = url()->query('/auth', [
+            'response_type' => 'code',
+            'me' => 'https://example.com',
+            'client_id' => 'https://app.example.com',
+            'redirect_uri' => 'https://app.example.com/callback',
+            'state' => '123456',
+            'scopes' => 'create update delete',
+            'code_challenge' => '123456',
+            'code_challenge_method' => 'invalid_value',
+        ]);
+
+        $response = $this->actingAs($user)->get($url);
+
+        $response->assertStatus(200);
+        $response->assertViewIs('indieauth.error');
+        $response->assertSee('only a code_challenge_method of "S256" is supported');
+    }
+}