Auth0 PHP API Integration

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

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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

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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

• /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

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

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>"]
}'

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>"]
}'

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

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>"

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.

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Common Mistakes

Mistake	Fix
Hardcoding domain or audience in source	Always read from environment variables - never embed credentials in code
Using STRATEGY_REGULAR for an API	API mode must use SdkConfiguration::STRATEGY_API - it disables sessions and cookies
Installing without a PSR-18 HTTP client	Must have guzzlehttp/guzzle or another PSR-18 client or the SDK cannot fetch JWKS
Not caching JWKS keys	Without a PSR-6 cache, the SDK fetches JWKS on every request - always configure tokenCache
Passing audience as a string	audience must be an array: ['https://my-api.example.com'] not 'https://my-api.example.com'
Passing domain as full URL with https://	domain should be the bare domain, e.g. my-tenant.us.auth0.com, not https://my-tenant.us.auth0.com
Using decode() without specifying token type	Always pass tokenType: Token::TYPE_ACCESS_TOKEN when manually calling decode()
Echoing exception messages to users	Use error_log() for the real error and return a generic JSON error message
Using an ID token instead of an access token	Must use the access token for API auth - ID tokens are for the client app
Created an Application instead of an API in Auth0	Must create an API resource (Applications -> APIs) - an Application doesn't issue access tokens with the right audience
Setting clientId and expecting RS256 to need it	For RS256, clientId is optional - the SDK validates against the JWKS endpoint
Using clientSecret for RS256 validation	clientSecret is only needed for HS256 - RS256 uses the public key from JWKS
Passing $_SERVER directly to getBearerToken()	The server param takes an array of key names to look up, e.g. ['HTTP_AUTHORIZATION'] - not $_SERVER itself

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Key SDK Methods

Method	Returns	Purpose
getBearerToken	?TokenInterface	Searches specified $_SERVER keys for a Bearer token, verifies signature, validates claims. Returns null if no token found or validation fails (does not throw).
decode	TokenInterface	Manually decodes and validates a JWT string
configuration	SdkConfiguration	Access the SDK configuration instance
Token::toArray	array	Returns all token claims as an associative array
Token::getSubject	?string	Returns the sub claim (user/client ID)
Token::getIssuer	?string	Returns the iss claim
Token::getAudience	?array	Returns the aud claim
Token::getExpiration	?int	Returns the exp claim (Unix timestamp)

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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

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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

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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

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References

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