Magento – How to write rest api for magento-1.9.

Magento 2 allows some web APIs to be accessed by unauthenticated (anonymous) users. Many of these APIs allow a customer to have a robust shopping experience on the website without having to log in.

Please check this link https://devdocs.magento.com/guides/v2.3/rest/anonymous-api-security.html

Preventing anonymous access to these endpoints could cause third-party integrations to fail. If a third-party integration calls any of these endpoints, it will receive an authentication error instead of the expected response. In this case, you might need to disable this feature.

To disable this feature, log in to the Admin panel and navigate to Stores > Settings > Configuration > Services > Magento Web API > Web API Security. Then select Yes from the Allow Anonymous Guest Access menu.

To check for a valid customer token Magento checks two criteria

1. Is token revoked ( That happens when user logout) : revoked is saved as 1 in oauth_token table
2. Token is actually present in oauth_token table

Magento runs a cron to remove the expired tokens (as per lifetime in admin setting) from the table (vendor\magento\module-integration\Cron\CleanExpiredTokens.php)

Possible solution

1. Increase Token lifetime from admin
2. Override the above mentioned cron to only remove the token that are revoked i.e the logged out customer tokens

Hope this answers your question