Get Refresh Token from LWA Authorization Code

lib/SellingPartnerOAuth.php

@@ -39,4 +39,42 @@ public static function getAccessTokenFromRefreshToken($refreshToken, $clientId,
 
         return $bodyAsJson['access_token'];
     }
+
+    /**
+     * @param string $lwaAuthorizationCode
+     * @param string $clientId
+     * @param string $clientSecret
+     * @param string $redirectUri
+     * @return string|null
+     * @throws GuzzleException
+     */
+    public static function getRefreshTokenFromLwaAuthorizationCode(
+        string $lwaAuthorizationCode,
+        string $clientId,
+        string $clientSecret,
+        string $redirectUri
+    ): ?string {
+        $client = new Client();
+        $params = [
+            'grant_type' => 'authorization_code',
+            'client_id' => $clientId,
+            'client_secret' => $clientSecret,
+            'code' => $lwaAuthorizationCode,
+            'redirect_uri' => $redirectUri,
+        ];
+        $options = array_merge([
+            RequestOptions::HEADERS => ['Accept' => 'application/json'],
+            RequestOptions::HTTP_ERRORS => false,
+            'curl' => [
+                CURLOPT_SSLVERSION => CURL_SSLVERSION_TLSv1_2,
+            ],
+        ], $params ? [RequestOptions::FORM_PARAMS => $params] : []);
+
+        $response = $client->request('POST', 'https://api.amazon.com/auth/o2/token', $options);
+
+        $body = $response->getBody()->getContents();
+        $bodyAsJson = json_decode($body, true);
+
+        return $bodyAsJson['refresh_token'];
+    }
 }