diff --git a/composer.json b/composer.json
index d04c792..3ab00c1 100644
--- a/composer.json
+++ b/composer.json
@@ -4,8 +4,8 @@
     "type": "library",
     "license": "Apache-2.0",
     "require": {
-        "novvor/identity-contracts": "^1.0",
-        "novvor/identity-sdk-php": "^1.0",
+        "novvor/identity-contracts": "^1.0 || ^2.0",
+        "novvor/identity-sdk-php": "^1.0 || ^2.0",
         "php": "^8.2"
     },
     "require-dev": {
diff --git a/src/FakeIdentityProvider.php b/src/FakeIdentityProvider.php
index e9444ea..9e90a53 100644
--- a/src/FakeIdentityProvider.php
+++ b/src/FakeIdentityProvider.php
@@ -5,14 +5,31 @@
 final class FakeIdentityProvider
 {
     /** @return array<string, mixed> */
-    public function discovery(string $issuer = 'https://identity.test'): array
+    public function discovery(string $issuer = 'https://identity.test', bool $highAssurance = false): array
     {
-        return [
+        $document = [
             'issuer' => $issuer,
             'authorization_endpoint' => $issuer.'/oauth/authorize',
             'token_endpoint' => $issuer.'/oauth/token',
+            'userinfo_endpoint' => $issuer.'/oauth/userinfo',
+            'introspection_endpoint' => $issuer.'/oauth/introspect',
+            'revocation_endpoint' => $issuer.'/oauth/revoke',
             'jwks_uri' => $issuer.'/.well-known/jwks.json',
+            'response_types_supported' => ['code'],
+            'response_modes_supported' => ['query'],
+            'grant_types_supported' => ['authorization_code', 'refresh_token', 'client_credentials'],
+            'token_endpoint_auth_methods_supported' => ['none', 'client_secret_post'],
             'code_challenge_methods_supported' => ['S256'],
+            'authorization_response_iss_parameter_supported' => true,
         ];
+        if ($highAssurance) {
+            $document['pushed_authorization_request_endpoint'] = $issuer.'/oauth/par';
+            $document['response_modes_supported'][] = 'query.jwt';
+            $document['token_endpoint_auth_methods_supported'][] = 'private_key_jwt';
+            $document['dpop_signing_alg_values_supported'] = ['RS256', 'ES256'];
+            $document['authorization_signing_alg_values_supported'] = ['RS256'];
+        }
+
+        return $document;
     }
 }
diff --git a/src/FakeOAuthEndpointError.php b/src/FakeOAuthEndpointError.php
new file mode 100644
index 0000000..72facd8
--- /dev/null
+++ b/src/FakeOAuthEndpointError.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Novvor\IdentitySdkTesting;
+
+final readonly class FakeOAuthEndpointError
+{
+    public function __construct(
+        public string $error,
+        public string $description,
+        public ?string $correlationId = null,
+        public ?string $dpopNonce = null,
+    ) {}
+
+    /** @return array{status: int, headers: array<string, string>, json: array{error: string, error_description: string}} */
+    public function response(int $status = 400): array
+    {
+        return [
+            'status' => $status,
+            'headers' => array_filter([
+                'X-Correlation-ID' => $this->correlationId,
+                'DPoP-Nonce' => $this->dpopNonce,
+            ], static fn (?string $value): bool => $value !== null && $value !== ''),
+            'json' => ['error' => $this->error, 'error_description' => $this->description],
+        ];
+    }
+}
diff --git a/tests/FakesTest.php b/tests/FakesTest.php
index b941090..eefc4d1 100644
--- a/tests/FakesTest.php
+++ b/tests/FakesTest.php
@@ -7,6 +7,7 @@
 use Novvor\IdentitySdkTesting\FakeBackChannelLogout;
 use Novvor\IdentitySdkTesting\FakeIdentityProvider;
 use Novvor\IdentitySdkTesting\FakeJwksDocument;
+use Novvor\IdentitySdkTesting\FakeOAuthEndpointError;
 use Novvor\IdentitySdkTesting\FakeStepUpSession;
 use PHPUnit\Framework\TestCase;
 
@@ -34,4 +35,29 @@ public function test_jwks_document_wraps_keys(): void
     {
         self::assertSame(['keys' => [['kid' => 'one']]], (new FakeJwksDocument([['kid' => 'one']]))->toArray());
     }
+
+    public function test_high_assurance_discovery_is_explicitly_opt_in(): void
+    {
+        $standard = (new FakeIdentityProvider())->discovery('https://identity.example.com');
+        $highAssurance = (new FakeIdentityProvider())->discovery('https://identity.example.com', true);
+
+        self::assertArrayNotHasKey('pushed_authorization_request_endpoint', $standard);
+        self::assertSame('https://identity.example.com/oauth/par', $highAssurance['pushed_authorization_request_endpoint']);
+        $authMethods = $highAssurance['token_endpoint_auth_methods_supported'] ?? null;
+        $responseModes = $highAssurance['response_modes_supported'] ?? null;
+        if (! is_array($authMethods) || ! is_array($responseModes)) {
+            self::fail('High-assurance discovery metadata must expose list capabilities.');
+        }
+        self::assertContains('private_key_jwt', $authMethods);
+        self::assertContains('query.jwt', $responseModes);
+    }
+
+    public function test_oauth_error_fake_never_contains_secrets(): void
+    {
+        $response = (new FakeOAuthEndpointError('use_dpop_nonce', 'Retry with the supplied nonce.', 'correlation-1', 'nonce-1'))->response();
+
+        self::assertSame(400, $response['status']);
+        self::assertSame('nonce-1', $response['headers']['DPoP-Nonce']);
+        self::assertArrayNotHasKey('access_token', $response['json']);
+    }
 }