How to Login into WordPress using Github - https://wparena.com/login-wordpress-using-github/

github-plugin-file.php

class GitHub_Login_Widget extends WP_Widget 
{
    public function __construct() 
    {
        parent::__construct( "Github_login_widget", "GitHub Login", array( "description" => __("Display a GitHub Login Button" ) ) );
    }

    public function form( $instance ) {

        if ( $instance )  {

            $title = esc_attr( $instance['title'] );
            $api_key = $instance['api_key'];
            $secret_key = $instance['secret_key'];
            $github_app_name = $instance['github_app_name'];

        } else {

            $title = '';
            $api_key = '';
            $secret_key = '';
            $github_app_name = '';

        }
        ?>

        <p>
            <label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php echo "Title"; ?></label>  
            <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo $title; ?>" />
        </p>

        <p>
            <label for="<?php echo $this->get_field_id( 'api_key' ); ?>"><?php echo "Client Id"; ?></label>
            <input type="text" class="widefat" id="<?php echo $this->get_field_id( 'api_key' ); ?>" name="<?php echo $this->get_field_name( 'api_key' ); ?>" value="<?php echo $api_key; ?>" />
        </p>

        <p>
            <label for="<?php echo $this->get_field_id( 'secret_key' ); ?>"><?php echo "Secret Key"; ?></label>
            <input type="text" class="widefat" id="<?php echo $this->get_field_id( 'secret_key' ); ?>" name="<?php echo $this->get_field_name( 'secret_key' ); ?>" value="<?php echo $secret_key; ?>" />
        </p>

        <p>
            <label for="<?php echo $this->get_field_id( 'github_app_name' ); ?>"><?php echo "App Name"; ?></label>
            <input type="text" class="widefat" id="<?php echo $this->get_field_id( 'github_app_name' ); ?>" name="<?php echo $this->get_field_name( 'github_app_name' ); ?>" value="<?php echo $github_app_name; ?>" />
        </p>

        <p>
            While creating a Github app use "<?php echo get_site_url() . '/wp-admin/admin-ajax.php?action=github_oauth_callback';  ?>" as callback URL.
        </p>

        <?php
    }

    public function update( $new_instance, $old_instance ) 
    {
        $instance = $old_instance;
        $instance['title'] = strip_tags( $new_instance['title'] );
        $instance['api_key'] = strip_tags( $new_instance['api_key'] );
        $instance['secret_key'] = strip_tags( $new_instance['secret_key'] );
        $instance['github_app_name'] = strip_tags( $new_instance['github_app_name'] );
        update_option( "github_key", $new_instance['api_key'] );
        update_option( "github_secret", $new_instance['secret_key'] );
        update_option( "github_app_name", $new_instance['github_app_name'] );
        return $instance;
    }

    public function widget( $args, $instance ) 
    {
        extract($args);

        $title = apply_filters( 'widget_title', $instance['title'] );
        echo $before_widget;

        if ( $title ) {
            echo $before_title . $title . $after_title ;
        }

        if ( is_user_logged_in() ) {
            ?>
                <a href="<?php echo wp_logout_url( get_permalink() ); ?>" title="Logout"><input type="button" value="Logout" /></a>
            <?php
        } else {
            ?>
                <a href="<?php echo site_url() . '/wp-admin/admin-ajax.php?action=github_oauth_redirect'; ?>"><input type="button" value="Login Using Github" /></a>
            <?php
        }
        echo $after_widget;
    }
}
register_widget( "GitHub_Login_Widget" );

github-rest-api-calls.php

    require_once( 'inc/githuboauth.php' );

    if( is_user_logged_in() ) 
    {
        //GET Request
        $response = GithubApiRequest( "https://api-url/", false, array("HTTP Header" => "HTTP Header Value", "HTTP Header" => "HTTP Header Value") );

        //POST Request
        $response = GithubApiRequest( "https://api-url/", array("Field Name" => "Field Value", "Field Name" => "Field Value"), array("HTTP Header" => "HTTP Header Value", "HTTP Header" => "HTTP Header Value") );        
    }