Add proxy selection capability

[anilnatha]

The organization I work for is using your WP Plugin. However, for it to work with our CAS server, we had to change a line of code in the class-authentication.php file that dealt with interfacing with a CAS server. Adding this customization prevented us from using the WP plugin update feature because it would overwrite our changes anytime Authorizer was updated.

I'm proposing this pull request that allows for a WP admin to choose how to interface with a CAS server, either over Proxy or using the Client method (see commits). I also added help documentation. These are demonstrated in the screenshots below. I have a limited understanding/knowledge of Authorizer and how CAS works, but did my best to add this functionality. Please feel free to share feedback as needed.

Option shown to WP Admin in the "External" tab of Authorizer:

Help documentation:

[figureone]

This looks great, thanks so much for your contribution! We'll review this week and let you know if we have any comments before merging.

Do you have a wordpress.org username so that we can add you to the list of Contributors?
https://wordpress.org/plugins/authorizer/#developers

[anilnatha]

You're very welcome, happy to contribute! Excited to hear what comes from the review, good or bad.

Here is my wordpress.org username slyraskal

[anilnatha]

One thing I should have mentioned, I defaulted the cas_method option to CLIENT since that's how this plugin has been working thus far. So current users of the plugin shouldn't be affected by this change, it will be seamless to them.

[figureone]

Aloha, looks really good! I made a few small changes, can you "Allow edits from maintainers" so I can push the commits to your pull request branch? Instructions here:
https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork

(Edit: never mind! GitHub Desktop told me I didn't have access, but I pushed the commits below successfully.)

[figureone]

We're releasing version 3.4.1 right now with your addition. Please let us know if you run into any issues.
https://wordpress.org/plugins/authorizer/

Thanks again, excellent work!

[anilnatha]

Hello,

Thank you for reviewing the changes and for listing me as a contributor. I've reviewed the additional changes you made to be better prepared for any future changes we may suggest.

I will leave my branch open until I've had a chance to deploy and test it using the WP plugin update feature.

Thanks again!