The easiest, non techie way is to add the ‘Redirect HTTP to HTTPS’ Extension kindly created by Greg Hogan (https://github.com/gregjhogan)

In the Azure Portal, select ‘Extensions’ in the App Service blade

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Add a new Extension by clicking on the ‘+Add’ button at the top
Select the ‘Redirect HTTP to HTTPS’ extension from the list given.

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Agree to the T&C’s
Wait till it’s installed and then restart the service (which you can find in the ‘Overview’)

After this when you access the website with http or without http/https, it will automatically redirect to https.