Daniel Westermann-Clark

The HTTP Authentication plugin allows you to use existing means of authenticating people to WordPress. This includes Apache’s basic HTTP authentication module, <a href="http://shibboleth.internet2.edu/" rel="nofollow ugc">Shibboleth</a>, and many others.
To follow updates to this plugin, visit:
https://danieltwc.com/
For help with this version, visit:
https://danieltwc.com/2011/http-authentication-4-0/

HTTP Authentication

Use an external authentication source in WordPress.

rtCamp

Shalin Shah

Nikhil Joshua

Chirag Mathur

Sagar Tamang

Ultra minimal plugin to let your users login to WordPress applications using their Google accounts. No more remembering hefty passwords!
<h3>Initial Setup</h3>
<ol>
<li>
Create a project from <a href="https://console.developers.google.com/apis/dashboard" rel="nofollow ugc">Google Developers Console</a> if none exists.
</li>
<li>
Go to Credentials tab, then create credential for OAuth client.
<ul>
<li>Application type will be Web Application</li>
<li>Add <code>YOUR_DOMAIN/wp-login.php</code> in Authorized redirect URIs</li>
</ul>
</li>
<li>
This will give you Client ID and Secret key.
</li>
<li>
Input these values either in <code>WP Admin > Settings > WP Google Login</code>, or in <code>wp-config.php</code> using the following code snippet:
<code>define( 'WP_GOOGLE_LOGIN_CLIENT_ID', 'YOUR_GOOGLE_CLIENT_ID' ); 
define( 'WP_GOOGLE_LOGIN_SECRET', 'YOUR_SECRET_KEY' );</code>
</li>
</ol>
<h3>Browser support</h3>
<a href="https://developers.google.com/identity/gsi/web/guides/supported-browsers" rel="nofollow ugc">These browsers are supported</a>. Note, for example, that One Tap Login is not supported in Safari.
<h3>How to enable automatic user registration</h3>
You can enable user registration either by 
– Enabling Settings > WP Google Login > Enable Google Login Registration
OR
<ul>
<li>Adding 
<code>define( 'WP_GOOGLE_LOGIN_USER_REGISTRATION', 'true' );</code> 
in wp-config.php file.</li>
</ul>
Note: If the checkbox is ON then, it will register valid Google users even when WordPress default setting, under
Settings > General Settings > Membership > Anyone can register checkbox
is OFF.
<h3>Restrict user registration to one or more domain(s)</h3>
By default, when you enable user registration via constant <code>WP_GOOGLE_LOGIN_USER_REGISTRATION</code> or enable Settings > WP Google Login > Enable Google Login Registration, it will create a user for any Google login (including gmail.com users). If you are planning to use this plugin on a private, internal site, then you may like to restrict user registration to users under a single Google Suite organization. This configuration variable does that.
Add your domain name, without any schema prefix and <code>www,</code> as the value of <code>WP_GOOGLE_LOGIN_WHITELIST_DOMAINS</code> constant or in the settings <code>Settings > WP Google Login > Whitelisted Domains</code>. You can whitelist multiple domains. Please separate domains with commas. See the below example to know how to do it via constants: 
 <code>define( 'WP_GOOGLE_LOGIN_WHITELIST_DOMAINS', 'example.com,sample.com' );</code>
Note: If a user already exists, they will be allowed to login with Google regardless of whether their domain is whitelisted or not. Whitelisting will only prevent users from registering with email addresses from non-whitelisted domains.
<h3>Hooks</h3>
For a list of all hooks please refer to <a href="https://github.com/rtCamp/login-with-google#hooks" rel="nofollow ugc">this documentation</a>.
<h4>wp-config.php parameters list</h4>
<ul>
<li>
<code>WP_GOOGLE_LOGIN_CLIENT_ID</code> (string): Google client ID of your application.
</li>
<li>
<code>WP_GOOGLE_LOGIN_SECRET</code> (string): Secret key of your application
</li>
<li>
<code>WP_GOOGLE_LOGIN_USER_REGISTRATION</code> (boolean) (optional): Set <code>true</code> If you want to enable new user registration. By default, user registration defers to <code>Settings > General Settings > Membership</code> if constant is not set.
</li>
<li>
<code>WP_GOOGLE_LOGIN_WHITELIST_DOMAINS</code> (string) (optional): Domain names, if you want to restrict login with your custom domain. By default, it will allow all domains. You can whitelist multiple domains.
</li>
</ul>
<h3>BTW, We’re Hiring!</h3>
<a href="https://rtcamp.com/careers/" rel="nofollow ugc"></a>

Log in with Google

In terms of ready-to-go possibilities, this plugin is the best free plugin for both Logging in and Registering with Google.

HTTP Authentication vs Log in with Google