So I abandoned the Auth0 plugin as their support team just let me know the WordPress plugin doesn't yet support SF Community as a Social provider.
Fortunately, I stumbled onto the miniOrange SAML WordPress plugin. The setup was incredibly easy and within an hour I was using my SF Community credentials to log into my WordPress site. As mentioned by @Developer_Wonk in the comments, you'll need to use SF as an Identity Provider. miniOrange provides instructions on setting that up to meet their plugin's needs.
Here's a quick run-down of the instructions:
- Install and activate the aforementioned plugin on your WordPress site.
- Under the Identity Provider tab, select Salesforce as the IdP. A link will appear with instructions on configuring SF as needed.
- Note: The instructions do leave out the steps regarding enabling SF as an Identity Provider. You will need to do this (under Administration Setup > Security Controls > Identity Provider) in order to complete Step 7. I had to create a new domain in order to enable it, which I hope was the right thing to do. I did not deploy the new domain to all users because I don't actually know what that will do. Looks like it wasn't necessary anyways.
- Once you have completed through step 7 outlined in the SF guide, step 8 will take you back to the WP plugin settings. The SAML Login URL can be found in the XML file that you downloaded in step 7, towards the bottom of the file. Be sure to grab the one ending with "HttpRedirect".
- The only thing I did differently from the instructions was to place
my new domain (from the note above) into the IdP Entity ID or Issuer
- I also made sure, under the General tab, to allow users to sign in using WordPress credentials to prevent myself from being accidentally locked out. The option isn't provided to site visitors, but they need to enter the URL displayed on that tab to bypass the SSO settings.
- Under the Attribute/Role Mapping tab, I did change the default settings. When you hit the Test configuration button at the top of the tab, it will show you which attributes are returned. I think it defaulted to NameID for Username and Email, which was not what I needed.
So far, this setup works. The only issue I've run into (and am waiting to hear back from their Support Team about), is that it isn't a single sign-out. If I can get that working (which is a requirement for my project), I will update this answer with the information.
It's also worth noting that I'm using a separate WP plugin called Force Login (by Kevin Vess) to...well, force users to login. No matter which page of my WP site you try to visit, it redirects to my SF Community login page.