diff --git a/README.md b/README.md
index 794fc95..a4d8ef6 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,36 @@
-# codepeak/oauth2-fortnox
+# Fortnox provider for league/oauth2-client
+
+This is a package to integrate [Fortnox](https://developer.fortnox.se/general/authentication/) authentication with the OAuth2 client library by [The League of Extraordinary Packages](https://github.com/thephpleague/oauth2-client).
+
+
+## Installation
+
+```bash
+composer require codepeak/oauth2-fortnox
+```
+
+## Usage
+
+### Create instance of the provider
+
+```php
+$provider = new \Codepeak\OAuth2\Client\Provider\Fortnox([
+    'clientId' => "YOUR_CLIENT_ID",
+    'clientSecret' => "YOUR_CLIENT_SECRET",
+    'redirectUri' => "http://your-redirect-uri"
+]);
+```
+
+### Get authorization URL
+
+```php
+$authorizationUrl = $provider->getAuthorizationUrl();
+```
+
+### Get the access token
+
+```php
+$token = $this->provider->getAccessToken("authorizaton_code", [
+    'code' => $_GET['code']
+]);
+```
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..d6a7518
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,24 @@
+{
+    "name": "codepeak/oauth2-fortnox",
+    "description": "A Fortnox provider for league/oauth2-client",
+    "license": "MIT",
+    "authors": [
+        {
+            "name": "Robert Lord, Codepeak AB",
+            "email": "robert@codepeak.se"
+        }
+    ],
+    "autoload": {
+        "psr-4": {
+            "Codepeak\\OAuth2\\Client\\": "src/"
+        }
+    },
+    "require": {
+        "php": ">=8.0",
+        "league/oauth2-client": "^2.6"
+    },
+    "suggest": {
+        "illuminate/support": "Laravel integration"
+    },
+    "minimum-stability": "dev"
+}
diff --git a/src/OptionProvider/FortnoxOptionProvider.php b/src/OptionProvider/FortnoxOptionProvider.php
new file mode 100644
index 0000000..1278930
--- /dev/null
+++ b/src/OptionProvider/FortnoxOptionProvider.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace Codepeak\OAuth2\Client\OptionProvider;
+
+use League\OAuth2\Client\OptionProvider\PostAuthOptionProvider;
+
+class FortnoxOptionProvider extends PostAuthOptionProvider
+{
+    protected string $base64AuthString = '';
+
+    public function __construct(string $base64AuthString = '')
+    {
+        $this->base64AuthString = $base64AuthString;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getAccessTokenOptions($method, array $params)
+    {
+        $options = parent::getAccessTokenOptions($method, $params);
+
+        $options['headers']['Authorization'] = 'Basic ' . $this->base64AuthString;
+
+        return $options;
+    }
+}
diff --git a/src/Provider/Fortnox.php b/src/Provider/Fortnox.php
new file mode 100644
index 0000000..ce47132
--- /dev/null
+++ b/src/Provider/Fortnox.php
@@ -0,0 +1,89 @@
+<?php
+
+namespace Codepeak\OAuth2\Client\Provider;
+
+use Codepeak\OAuth2\Client\OptionProvider\FortnoxOptionProvider;
+use League\OAuth2\Client\Provider\AbstractProvider;
+use League\OAuth2\Client\Provider\Exception\IdentityProviderException;
+use League\OAuth2\Client\Token\AccessToken;
+use Psr\Http\Message\ResponseInterface;
+
+class Fortnox extends AbstractProvider
+{
+    public function __construct(array $options = [], array $collaborators = [])
+    {
+        $this->fillProperties($options);
+
+        $collaborators['optionProvider'] = new FortnoxOptionProvider(
+            base64_encode($this->clientId . ':' . $this->clientSecret)
+        );
+
+        parent::__construct($options, $collaborators);
+    }
+
+    public function getBaseAuthorizationUrl(): string
+    {
+        return 'https://apps.fortnox.se/oauth-v1/auth';
+    }
+
+    public function getBaseAccessTokenUrl(array $params): string
+    {
+        return 'https://apps.fortnox.se/oauth-v1/token';
+    }
+
+    /**
+     * Returns the string that should be used to separate scopes when building
+     * the URL for requesting an access token.
+     *
+     * @return string Scope separator
+     */
+    protected function getScopeSeparator()
+    {
+        return ' ';
+    }
+
+    protected function getAuthorizationParameters(array $options)
+    {
+        $options = parent::getAuthorizationParameters($options);
+
+        // Add offline access type
+        if (! isset($options['access_type'])) {
+            $options['access_type'] = 'offline';
+        }
+
+        // Remove approval_prompt since Fortnox forces approval
+        unset($options['approval_prompt']);
+
+        return $options;
+    }
+
+    public function getResourceOwnerDetailsUrl(AccessToken $token)
+    {
+        return '';
+    }
+
+    protected function getDefaultScopes()
+    {
+        return [];
+    }
+
+    protected function checkResponse(ResponseInterface $response, $data)
+    {
+        $statusCode = $response->getStatusCode();
+        if ($statusCode >= 400) {
+            $message = $response->getReasonPhrase();
+            if (isset($data['error_description'])) {
+                $message = $data['error_description'];
+            }
+            throw new IdentityProviderException(
+                $message,
+                $statusCode,
+                $response
+            );
+        }
+    }
+
+    protected function createResourceOwner(array $response, AccessToken $token)
+    {
+    }
+}