Jonatha, jayanta,
I think the documentation should say:
Verify that you have a website running on port 80 or HTTPS is enabled on port 443. This is to accommodate the variety of encrypted and unencrypted calls made to Portal for ArcGIS. ArcGIS Web Adaptor cannot be configured with your portal if it is deployed on a website running on ports other than 80 or 443. For instructions on how to create a website, consult the product documentation specific for your Java application server. For more information about setting up and using HTTPS, see Enable HTTPS on your web server.
but documentation for arcgis 10.6, still say
Verify that you have a website running on port 80 and HTTPS is enabled on port 443. This is to accommodate the variety of encrypted and unencrypted calls made to Portal for ArcGIS. ArcGIS Web Adaptor cannot be configured with your portal if it is deployed on a website running on ports other than 80 and 443. For instructions on how to create a website, consult the product documentation specific for your Java application server. For more information about setting up and using HTTPS, see Enable HTTPS on your web server.