I have a client who wants to accept Authorize.net donations on their website. We only have a need for one page to be secured for our purposes. I've put a lot of research into this and it seems that the Wordpress HTTPS plugin would be the best option, with the least amount of brain damage. However, I see that the plugin has not been updated in three years. Multiple forums and blogs say that it is still safe to use, but I want to know if anyone has/is currently using this plugin for similar purposes and if they have any advice for me before I go down this road? Thank you!
If you are looking to use HTTPS, I reccomend following this wordpress guide: https://make.wordpress.org/support/user-manual/web-publishing/https-for-wordpress/#implementing-https-for-wordpress
You can get a free SSL Certificate from: https://letsencrypt.org/ If you find difficulty setting it up, you can often pay your host a small fee to help set this up. Once set up, you just need to make sure all the links on the page are HTTPS and not HTTP. Really easy to fix with plugins like Velvet Blues URL.
The Wordpress HTTPS plugin just makes implementing the SSL a bit easier. I would discourage installing old plugins as they often have security flaws and can conflict with your theme / other plugins.
Wordpress HTTPS doesn't solely secure the site. It just allows a page/pages/sections to be forced to HTTPs. You still need a certificate.
Our company uses Wordpress HTTPS in combination with an SSL certificate installed to the server. We also process through Authorize.net, and have not experienced issues (WP 4.4.2); though, we're still updating our theme to be compatible with 4.5.x.
There is a Woocommerce setting to force SSL on the checkout page only. It's in
Woocommerce > settings > checkout > Force secure checkout
As a side note, and someone correct me if I'm wrong on this, but I've recently heard that it actually doesn't matter if the page is loaded over https as the only connection that has to be a secure ssl connection is the one from the client's computer to authorize.net. Having the server send content to the user over https is just for show because everyone thinks this means their checkout is secure.