Mixed content issue- Content must be served as HTTPS || Lumen || Swagger API

Mixed Content: The page at 'https://api.xyz.com/api/documentation' was loaded over HTTPS,

but requested an insecure stylesheet 'http://api.xyz.com/swagger-ui-assets/swagger-ui.css?v=26ec363936a21921c9fec290e551e3eb'.

This request has been blocked; the content must be served over HTTPS.

I know how to solve this problem in Laravel but unable to solve this in case of Lumen.

Tried Solutions:

1. Added below line in AppServiceProvider

   URL::forceSchema('https');  
   
   

via Chebli Mohamed