Auth Token

Overview

The Auth Token integration enables single sign-on (SSO) between your platform and Publica.la stores. Users authenticated in your system (LMS, e-commerce, CMS, etc.) can access Publica.la content without logging in again.

How it works: Your platform generates a signed JWT containing user information, redirects the user to Publica.la with that token, and we validate it to grant access automatically. New users are created on first authentication; existing users are recognized by their uuid.

Not the right fit? Consider IP Authentication for IP-based access, LTI for LMS integrations, or URL Referrer for domain or URL-based access.

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Setup

1. Generate a secret key — Create a 32-character secret that you'll use to sign JWTs.

2. Contact support with the following configuration:

   Parameter	Description
   key	The 32-character secret you generated
   issuer	Your platform identifier (e.g., platform-name). Must match iss claim in tokens.
   redirect_url	Where to send users on auth errors
   logout_url	Where to send users after logging out

3. Wait for confirmation before testing your integration.

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Token format

Tokens must be signed with HS256 (HMAC-SHA256). Other algorithms are rejected.

Example payload

{
  "iss": "platform-name",
  "aud": "farfalla",
  "sub": "user",
  "jti": "550e8400-e29b-41d4-a716-446655440000",
  "exp": 1699999960,
  "user": {
    "uuid": "user-123",
    "email": "user@example.com",
    "picture_url": "https://example.com/avatar.jpg"
  },
  "intended_url": "https://store.publica.la/reader/my-ebook"
}

Claims reference

Required JWT claims

Claim	Type	Description
iss	string	Your platform identifier. Must match configured issuer.
aud	string	Must be "farfalla".
sub	string	Must be "user".
jti	string	Unique token ID. Use UUID v4 to prevent replay.
exp	number	Expiration timestamp (Unix time). We recommend 60 seconds for real-time redirects.

User object (user claim)

Field	Required	Type	Description
uuid	Yes	string	Unique identifier for the user in your system. 1-200 characters. Stored as external_id in Publica.la.
email	No	string	User's email address. Must be valid format if provided. Updated on each login if changed.
picture_url	No	string	Profile picture URL. Max 200 characters. Only set on first login, not updated afterwards.
accept_terms_and_policies	No	boolean	If true, automatically accepts terms on first login.

Optional claims

Claim	Type	Description
intended_url	string	Where to redirect after successful login. Must be a valid URL. Defaults to /library.
reader_exit_url	string	Custom URL for the reader's exit button. Stored in session for the reader to use.

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Endpoint

URL

https://{store-domain}/auth/token

Methods

Both GET and POST are supported.

Passing the token

The token can be provided in two ways:

Query Parameter

https://{store-domain}/auth/token?external-auth-token={JWT}

Recommended for browser redirects. JWT tokens are URL-safe, no encoding needed.

Security consideration

Tokens in URLs appear in browser history, server logs, and may leak via Referrer headers. Use short expiration times (60 seconds) to mitigate risk.

HTTP Header

GET /auth/token HTTP/1.1
Host: {store-domain}
external-auth-token: {JWT}

More secure as tokens don't appear in logs or browser history. Requires JavaScript or server-side implementation.

Response behavior

Scenario	HTTP Response	Destination
Valid token	302 Redirect	intended_url from token, or /library if not specified
Invalid token	302 Redirect	redirect_url with error query params
Invalid user data	302 Redirect	redirect_url with error query params
Missing store configuration	422 JSON	Error message returned

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User management

View detailed authentication flow

New users

When a user authenticates for the first time (no existing user with that uuid):

1. A new user account is created with the provided uuid as external_id
2. email and picture_url are set if provided in the token
3. If accept_terms_and_policies: true, terms are automatically accepted
4. User is logged in and redirected to their destination

Returning users

When a user with an existing uuid authenticates:

1. User is found by their external_id (your uuid)
2. email is updated if the token contains a different value
3. picture_url is not updated (only set on creation)
4. User is logged in and redirected

Email uniqueness

Each email address can only be associated with one uuid. If you send an email that already belongs to a different user, authentication will fail with an invalid-user error.

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Code examples

PHP (lcobucci/jwt v5)

use Lcobucci\JWT\Configuration;
use Lcobucci\JWT\Signer\Hmac\Sha256;
use Lcobucci\JWT\Signer\Key\InMemory;
use DateTimeImmutable;

$config = Configuration::forSymmetricSigner(
    new Sha256(),
    InMemory::plainText($_ENV['JWT_SECRET'])
);

$now = new DateTimeImmutable();

$token = $config->builder()
    ->issuedBy('platform-name')                      // iss - must match configured issuer
    ->permittedFor('farfalla')                       // aud - always "farfalla"
    ->relatedTo('user')                              // sub - always "user"
    ->identifiedBy(bin2hex(random_bytes(16)))        // jti - unique token ID
    ->expiresAt($now->modify('+60 seconds'))         // exp - short expiration for security
    ->withClaim('user', [
        'uuid' => $userId,
        'email' => $userEmail,
        'picture_url' => $userAvatar,
    ])
    ->withClaim('intended_url', 'https://store.publica.la/reader/my-ebook')
    ->getToken($config->signer(), $config->signingKey());

$jwt = $token->toString();

// Redirect user to Publica.la
header('Location: https://store.publica.la/auth/token?external-auth-token=' . $jwt);
exit;

Node.js

const jwt = require('jsonwebtoken');
const crypto = require('crypto');

const token = jwt.sign(
  {
    iss: 'platform-name',        // must match configured issuer
    aud: 'farfalla',             // always "farfalla"
    sub: 'user',                 // always "user"
    jti: crypto.randomUUID(),    // unique token ID
    user: {
      uuid: userId,
      email: userEmail,
      picture_url: userAvatar,
    },
    intended_url: 'https://store.publica.la/reader/my-ebook',
  },
  process.env.JWT_SECRET,
  {
    algorithm: 'HS256',
    expiresIn: 60,               // 60 seconds
  }
);

// Redirect user to Publica.la
res.redirect(`https://store.publica.la/auth/token?external-auth-token=${token}`);

Python

import jwt
import os
from uuid import uuid4
from time import time

token = jwt.encode(
    {
        'iss': 'platform-name',      # must match configured issuer
        'aud': 'farfalla',           # always "farfalla"
        'sub': 'user',               # always "user"
        'jti': str(uuid4()),         # unique token ID
        'exp': int(time()) + 60,     # 60 seconds from now
        'user': {
            'uuid': user_id,
            'email': user_email,
            'picture_url': user_avatar,
        },
        'intended_url': 'https://store.publica.la/reader/my-ebook',
    },
    os.environ['JWT_SECRET'],
    algorithm='HS256'
)

# Redirect user to Publica.la
return redirect(f'https://store.publica.la/auth/token?external-auth-token={token}')

---

Error handling

When authentication fails, users are redirected to your configured redirect_url with error information in query parameters:

https://your-redirect-url.com?external-auth-token-error={code}&external-auth-token-error-details={base64-json}

Error codes

Code	Description
invalid-token	Token validation failed (expired, bad signature, wrong issuer/audience/subject)
invalid-user	User data validation failed (invalid email format, missing uuid, uuid too long)

Decoding error details

The external-auth-token-error-details parameter contains Base64-encoded JSON with specific error messages:

JavaScript

const details = JSON.parse(atob(errorDetails));
console.log(details);

PHP

$details = json_decode(base64_decode($errorDetails), true);
print_r($details);

Python

import base64
import json

details = json.loads(base64.b64decode(error_details))
print(details)

Example error responses

Token validation error:

{
  "token": {
    "exp": "Token is expired or `exp` attribute not present."
  }
}

User validation error:

{
  "email": ["The email must be a valid email address."]
}

Email conflict error:

{
  "uuid": ["This email is already attached to UUID abc-123."]
}

---

Troubleshooting

Problem	Cause	Solution
"Token is expired"	exp timestamp is in the past	Ensure server clock is synchronized (NTP). Use 60-second expiration.
"Invalid signature"	Signing key doesn't match	Verify key matches exactly what was configured in setup.
"Invalid issuer"	iss claim mismatch	Ensure iss matches the configured issuer exactly (case-sensitive).
"Invalid audience"	aud claim wrong	Must be exactly "farfalla".
"Email already attached to UUID"	Email registered to different user	Use the correct uuid for that email, or use a different email.
422 error	Store not configured	Contact support to complete Auth Token setup.

Debugging tips

1. Inspect your token — Paste it at jwt.io to see decoded header and payload
2. Check expiration — Ensure exp is in the future when the request reaches Publica.la
3. Verify fixed values — aud must be "farfalla", sub must be "user"
4. Decode errors — Use base64decode.org to read error details

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JWT Generator

Generate test tokens to verify your integration:

Payload (JSON){ "iss": "platform-name", "aud": "farfalla", "sub": "user", "jti": "8bda37a5-3580-4b23-8fbb-659c98f6d9e5", "iat": 1765530813, "exp": 1765534413, "user": { "uuid": "user-123", "email": "user@example.com" } }

Secret Key

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Security best practices

1. Use short expiration times — 60 seconds is recommended for tokens passed in URLs
2. Store secrets securely — Use environment variables, never commit keys to version control
3. Use HTTPS only — Never transmit tokens over unencrypted connections
4. Prefer headers when possible — HTTP headers don't appear in browser history or server logs
5. Generate unique jti values — Use UUID v4 for each token to enable replay detection
6. Rotate keys periodically — Contact support to update your signing key

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Tips for integrators

• Anonymous users — Omit email to create anonymous user accounts
• Direct content access — Use intended_url to send users directly to a specific book or page
• Custom reader exit — Use reader_exit_url to control where users go when closing the reader
• No URL encoding needed — JWT tokens are URL-safe by design
• Email updates — Users are matched by uuid, so if an email changes in your system, just send the new email and it will be updated automatically