For Core apps, UseHttpsRedirection middleware can be used to force https by adding app.UseHttpsRedirection(); to the program.cs as in the example below
Securing domain pointers with a single domain certificate
Because multi-domain certificates can be cost prohibitive or less than straight forward to order, a workaround is using domain forwarding and flexible SSL through cloudflare.com. Flexible SSL means the connection is secure between the client and cloudflare, but is not secure between cloudflare and the site. So it shouldn't, for example, be used to secure a subdirectory pointer. But is sufficient when a domain pointer is only an alternate address for a site. Please note that this will assume some familiarity with cloudflare since it is an external service.
Add the domain pointer as a website in cloudflare and then when viewing the domain Overview, expand SSL, click Overview, then Configure, select the Flexible radial button and then Save.
Now create the domain forwarding rule by expanding Rules then clicking Page Rules.
In the URL field enter the domain being forwarded.
For Then the settings are select "Forwarding URL" and "301 - Permanent Redirect" and enter the primary site domain in the "Enter destination URL" field.
Save and Deploy
After creating a rule for the root domain, create a second rule for URL "www.forwardedDomain.com" or "*.forwardedDomain.com" with the same destination URL.