Auth0 PHP API Integration

Protect PHP API endpoints with JWT access token validation using auth0/auth0-php in API mode (STRATEGY_API).

Prerequisites

• PHP 8.2+ with extensions: mbstring, openssl, json
• Composer installed
• Auth0 API resource configured (not an Application - must be an API)
• If you don't have Auth0 set up yet, use the auth0-quickstart skill first

When NOT to Use

• PHP web applications with login/logout flows - Use auth0-php for session-based authentication
• Laravel applications - Use auth0/laravel-auth0 which has built-in API guard support
• Symfony applications - Use auth0/symfony with its security bundle
• Single Page Applications - Use auth0-react, auth0-vue, or auth0-angular for client-side auth
• Issuing tokens - This skill is for validating access tokens, not issuing them

Quick Start Workflow

1. Install SDK

composer require auth0/auth0-php vlucas/phpdotenv guzzlehttp/guzzle guzzlehttp/psr7 "symfony/cache:^7.0"

• auth0/auth0-php - The Auth0 SDK (v8.x)
• vlucas/phpdotenv - Load .env files into $_ENV
• guzzlehttp/guzzle + guzzlehttp/psr7 - PSR-18 HTTP client required by the SDK
• symfony/cache - PSR-6 cache for JWKS key caching (recommended for production)

2. Create Auth0 API

You need an API (not Application) in Auth0.

STOP - ask the user before proceeding.

Ask exactly this question and wait for their answer before doing anything else:

"How would you like to create the Auth0 API resource?

1. Automated - I'll run Auth0 CLI scripts that create the resource and write the exact values to your .env automatically.
2. Manual - You create the API yourself in the Auth0 Dashboard (or via auth0 apis create) and provide me the Domain and Audience.

Which do you prefer? (1 = Automated / 2 = Manual)"

Do NOT proceed to any setup steps until the user has answered. Do NOT default to manual.

If the user chose Automated, follow the Setup Guide for complete CLI scripts. The automated path writes .env for you - skip Step 3 below and proceed directly to Step 4.

If the user chose Manual, follow the Setup Guide (Manual Setup section) for full instructions. Then continue with Step 3 below.

Quick reference for manual API creation:

# Using Auth0 CLI
auth0 apis create \
  --name "My PHP API" \
  --identifier https://my-api.example.com \
  --json

Or create manually in Auth0 Dashboard -> Applications -> APIs

3. Configure Environment

Create .env:

AUTH0_DOMAIN=your-tenant.us.auth0.com
AUTH0_AUDIENCE=https://your-api.example.com

AUTH0_DOMAIN is your Auth0 tenant domain (without https://). AUTH0_AUDIENCE is the API identifier you set when creating the API resource in Auth0.

4. Initialize Auth0 in API Mode

Create auth0.php to initialize the SDK:

<?php

require 'vendor/autoload.php';

use Auth0\SDK\Auth0;
use Auth0\SDK\Configuration\SdkConfiguration;
use Symfony\Component\Cache\Adapter\FilesystemAdapter;

$dotenv = Dotenv\Dotenv::createImmutable(__DIR__);
$dotenv->load();

$configuration = new SdkConfiguration(
    strategy: SdkConfiguration::STRATEGY_API,
    domain: $_ENV['AUTH0_DOMAIN'],
    clientId: null,
    audience: [$_ENV['AUTH0_AUDIENCE']],
    tokenAlgorithm: 'RS256',
    tokenCache: new FilesystemAdapter('auth0_jwks', 600, __DIR__ . '/var/cache'),
    tokenCacheTtl: 600,
);

$auth0 = new Auth0($configuration);

Key differences from web app mode:

• STRATEGY_API - stateless, no sessions or cookies
• clientId is not required for RS256 validation (only needed for HS256)
• audience accepts an array of allowed audience strings
• tokenCache is a PSR-6 CacheItemPoolInterface for JWKS caching

5. Create Middleware Function

Since the SDK does not include a built-in middleware, create a reusable guard function. Create middleware.php:

<?php

use Auth0\SDK\Auth0;
use Auth0\SDK\Token;
use Auth0\SDK\Exception\InvalidTokenException;

function requireAuth(Auth0 $auth0, ?array $requiredScopes = null): array
{
    $token = $auth0->getBearerToken(
        server: ['HTTP_AUTHORIZATION']
    );

    if ($token === null) {
        http_response_code(401);
        header('Content-Type: application/json');
        echo json_encode(['error' => 'unauthorized', 'message' => 'Missing or invalid Bearer token']);
        exit;
    }

    $claims = $token->toArray();

    if ($requiredScopes !== null) {
        $grantedScopes = isset($claims['scope']) ? explode(' ', $claims['scope']) : [];
        $missingScopes = array_diff($requiredScopes, $grantedScopes);

        if (!empty($missingScopes)) {
            http_response_code(403);
            header('Content-Type: application/json');
            echo json_encode(['error' => 'insufficient_scope', 'message' => 'Token lacks required scopes']);
            exit;
        }
    }

    return $claims;
}

getBearerToken() searches for a Bearer token at the locations you specify, verifies the signature against the JWKS endpoint, and validates claims (issuer, audience, expiration). The server parameter is an array of $_SERVER key names to check (e.g., ['HTTP_AUTHORIZATION']) - not $_SERVER itself. Returns a TokenInterface on success or null if no valid token is found (does not throw).

6. Create API Routes

Create index.php as a front controller:

<?php

require 'auth0.php';
require 'middleware.php';

$method = $_SERVER['REQUEST_METHOD'];
$path = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);

header('Content-Type: application/json');

switch ($path) {
    case '/api/public':
        echo json_encode(['message' => 'Public endpoint - no authentication required']);
        break;

    case '/api/private':
        $claims = requireAuth($auth0);
        echo json_encode(['message' => 'Private endpoint', 'sub' => $claims['sub']]);
        break;

    case '/api/private-scoped':
        $claims = requireAuth($auth0, ['read:messages']);
        echo json_encode(['messages' => [], 'sub' => $claims['sub']]);
        break;

    default:
        http_response_code(404);
        echo json_encode(['error' => 'not_found']);
        break;
}

7. Access Token Claims

The decoded JWT claims are returned as an associative array:

$claims = requireAuth($auth0);

$userId = $claims['sub'];       // user/client ID
$scopes = $claims['scope'];     // space-separated granted scopes
$issuer = $claims['iss'];       // issuer (your Auth0 domain URL)
$audience = $claims['aud'];     // audience (string or array)
$expiration = $claims['exp'];   // expiration timestamp

You can also use the Token object's typed accessor methods:

$token = $auth0->getBearerToken(server: ['HTTP_AUTHORIZATION']);
if ($token !== null) {
    $subject = $token->getSubject();     // returns ?string
    $issuer = $token->getIssuer();       // returns ?string
    $audience = $token->getAudience();   // returns ?array
    $expiration = $token->getExpiration(); // returns ?int
}

8. Add CORS Headers

When your API receives requests from a browser-based SPA, add CORS headers. Create cors.php:

<?php

function handleCors(array $allowedOrigins): void
{
    $origin = $_SERVER['HTTP_ORIGIN'] ?? '';

    if (in_array($origin, $allowedOrigins, true)) {
        header("Access-Control-Allow-Origin: $origin");
        header('Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS');
        header('Access-Control-Allow-Headers: Authorization, Content-Type');
        header('Access-Control-Max-Age: 86400');
    }

    if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
        http_response_code(204);
        exit;
    }
}

Then add these lines at the top of index.php, before the existing require 'auth0.php' line:

require 'cors.php';
handleCors(['https://your-spa-domain.com']);

The updated index.php head should be:

<?php

require 'cors.php';
handleCors(['https://your-spa-domain.com']);

require 'auth0.php';
require 'middleware.php';

// ... rest of index.php

CORS must be handled before auth so that preflight OPTIONS requests short-circuit without triggering token validation.

9. Test the API

Agent instruction: Start the PHP built-in server and verify the basic endpoints work without credentials:

php -S localhost:8000 index.php &
sleep 1
curl -s http://localhost:8000/api/public
curl -s -o /dev/null -w "%{http_code}" http://localhost:8000/api/private

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• /api/public should return {"message":"Public endpoint - no authentication required"}
• /api/private should return HTTP 401

If both pass, the middleware is working. Kill the background server when done:

kill %1 2>/dev/null

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Failcheck: If the server fails to start or /api/public errors, check for PHP syntax issues or missing .env. After 5-6 failed iterations, use AskUserQuestion to ask the user for more details about their environment.

Agent instruction: STOP - ask after basic tests pass.

Once public/401 tests pass, ask the user:

"Your API is set up and the middleware is working (public returns 200, private returns 401 without a token). Would you like me to help you set up testing with a real access token?

1. Yes - I'll help you configure an M2M application to get test tokens.
2. No - I'm done for now.

Which do you prefer?"

Do NOT proceed with M2M/token setup unless the user says yes. If they say no, summarize what was done and stop.

Agent instruction (M2M app setup - only if user wants testing):

If the user chose to set up testing, ask:

"To test your protected endpoints, you need a Machine-to-Machine (M2M) application authorized to request tokens for this API.

1. Create new - I'll create a new M2M application and authorize it for this API.
2. Use existing - You already have an M2M application. Provide the Client ID and I'll authorize it for this API.

Which do you prefer? (1 = Create new / 2 = Use existing)"

Do NOT proceed until the user answers. Do NOT silently pick an existing application from the tenant.

If the user chose "Create new":

auth0 apps create \
  --name "${PWD##*/} (Test App)" \
  --type m2m \
  --no-input --json

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Parse the JSON with jq to extract client_id. Do NOT use --reveal-secrets - never expose client secrets in agent context. Then create a client grant:

auth0 api post "client-grants" --data '{
  "client_id": "<CLIENT_ID>",
  "audience": "<API_IDENTIFIER>",
  "scope": ["<SCOPES>"]
}'

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If the user chose "Use existing": Ask for the Client ID. Then create a client grant to authorize it for this API:

auth0 api post "client-grants" --data '{
  "client_id": "<USER_PROVIDED_CLIENT_ID>",
  "audience": "<API_IDENTIFIER>",
  "scope": ["<SCOPES>"]
}'

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If the grant already exists (409 conflict), that's fine - the app is already authorized.

Agent instruction (TOKEN ISOLATION - CRITICAL):

The agent MUST NEVER directly see or display access token values. Token security rules:

• Do NOT run auth0 test token on its own - it outputs the token to stdout
• Do NOT ask the user to paste their token into the conversation
• Do NOT echo, print, or log the token value
• Do NOT store the token in a file

Secure testing approach (single-command chain):

If the user explicitly asks to test the protected endpoints, use a single-command chain that captures the token into a shell variable and immediately uses it:

php -S localhost:8000 index.php &
sleep 1
TEST_TOKEN=$(auth0 test token <M2M_CLIENT_ID> --audience <AUDIENCE> --scopes <SCOPE1,SCOPE2> 2>/dev/null | grep -o 'ey[A-Za-z0-9_-]*\.[A-Za-z0-9_-]*\.[A-Za-z0-9_-]*') && \
[ -n "$TEST_TOKEN" ] && echo "Token acquired (${#TEST_TOKEN} chars)" && \
echo "=== GET /api/private ===" && \
curl -s http://localhost:8000/api/private -H "Authorization: Bearer $TEST_TOKEN" && \
echo "" && echo "=== GET /api/private-scoped ===" && \
curl -s http://localhost:8000/api/private-scoped -H "Authorization: Bearer $TEST_TOKEN"
kill %1 2>/dev/null

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Rules:

1. ONLY use when the user explicitly asks to test
2. Always chain token acquisition + curl in a SINGLE && command
3. NEVER add echo $TEST_TOKEN or any command that would print the raw token value
4. If the token acquisition fails (empty variable), report that the M2M app may not be authorized
5. Client ID is REQUIRED - if M2M setup was not completed, ask the user first

If the user does NOT ask to test, just provide the commands for them to run manually:

auth0 test token <CLIENT_ID> --audience <AUDIENCE> --scopes <SCOPE1,SCOPE2>
curl http://localhost:8000/api/private -H "Authorization: Bearer <PASTE_TOKEN_HERE>"

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Start the server:

php -S localhost:8000 index.php

Test public endpoint (no token needed):

curl http://localhost:8000/api/public

Test protected endpoint without token (should return 401):

curl http://localhost:8000/api/private

Test protected endpoint with token:

curl http://localhost:8000/api/private \
  -H "Authorization: Bearer YOUR_ACCESS_TOKEN"

Test scoped endpoint:

curl http://localhost:8000/api/private-scoped \
  -H "Authorization: Bearer YOUR_ACCESS_TOKEN"

Get a test token via Auth0 Dashboard -> APIs -> Test tab, or via the M2M flow described above.

Common Mistakes

Key SDK Methods

Related Skills

• auth0-php - For PHP web apps with login/logout using session-based auth
• auth0-quickstart - Basic Auth0 setup and framework detection
• auth0-cli - Manage Auth0 resources from the terminal
• auth0-mfa - Add Multi-Factor Authentication

Quick Reference

SdkConfiguration for APIs:

$configuration = new SdkConfiguration(
    strategy: SdkConfiguration::STRATEGY_API,       // required - stateless mode
    domain: $_ENV['AUTH0_DOMAIN'],                   // required
    audience: [$_ENV['AUTH0_AUDIENCE']],             // required - array of identifiers
    tokenAlgorithm: 'RS256',                        // default
    tokenCache: $psrCacheAdapter,                    // recommended for production
    tokenCacheTtl: 600,                             // JWKS cache TTL in seconds
);

Token validation:

$token = $auth0->getBearerToken(server: ['HTTP_AUTHORIZATION']);  // returns ?TokenInterface
$claims = $token->toArray();                         // all claims as array
$userId = $token->getSubject();                      // sub claim

Manual decode:

use Auth0\SDK\Token;

$token = $auth0->decode(
    $jwtString,
    tokenType: Token::TYPE_ACCESS_TOKEN,
);

Environment variables:

• AUTH0_DOMAIN - your Auth0 tenant domain (e.g. tenant.us.auth0.com)
• AUTH0_AUDIENCE - your API identifier (e.g. https://api.example.com)

Common Use Cases:

• Protect routes -> requireAuth($auth0) (see Step 5)
• Scope enforcement -> requireAuth($auth0, ['read:messages']) (see Step 5)
• CORS setup -> Integration Guide
• Multi-audience validation -> Integration Guide
• Advanced configuration -> API Reference

Detailed Documentation

• Setup Guide - Auth0 CLI setup, environment configuration, getting test tokens
• Integration Guide - Scopes, permissions, middleware, multi-audience, CORS, error handling
• API Reference - Complete SDK API for API mode, configuration options, token methods

References

• auth0/auth0-php on Packagist
• auth0/auth0-PHP on GitHub
• Auth0 PHP API Quickstart
• PHP Documentation
• Access Tokens Guide