There are a few simple free plugins as well as paid plugins to make your website password protected.
Password Protected – Free
Learn more detail here: http://wordpress.org/plugins/password-protected/
A very simple way to quickly password protect your WordPress site with a single password.
This plugin only protects your WordPress content. It does not protect and images or uploaded files so if you enter and exact URL to in image file it will still be accessible.
Password protect your WordPress site with a single password.
Option to allow access to feeds.
Option to allow administrators access without entering password.
Works with Mark Jaquith’s Login Logo plugin.
Works with the Uber Login Logo plugin.
Private Blog – Free
Learn more detail here: https://www.volcanicpixels.com/password-protect-wordpress-plugin/
Want to make all or part of your WordPress website private? With support for; multiple passwords, upload protection, RSS feed protection, access logs and much more, we’ve got you covered.
Password Protect – $19
Learn more detail here: https://premium.wpmudev.org/project/password-protect-selected-content/
Password protect allows you to easily hide content in any post or page behind a safe and secure password, no complex membership system required.
Just select the content you’d like to hide (it can be a video, audio track, paragraph, answer or anything else at all), click on the lock button and select a password that must be entered.
Once activated you’ll see a nice new ‘Password Protect’ icon added to your Visual editor that you can use to password protect selected content.
Secure Client Portal & Invoicing – Starts from $59
Learn more detail here: http://wp-client.com/
One plugin configures multiple areas of your WordPress installation and allows the site Administrator to easily create new Client Areas, Client Management Portals, Client Estimates & Invoices, Client File Upload Areas, or Private Staff Pages on the site by entering just a few data fields. Additionally, clients can upload/download secure files.
Restrict Content Pro – Starts from $29
Restrict Content Pro allows you to accept credit cards through your Braintreepayments.com account during the user registration process.
When using this add-on, your subscribers will stay on your site throughout the entire registration process, instead of being redirected to an outside site, such as PayPal. The user simply enters their credit card information and clicks Register.
Allow users to pay for subscriptions with credit cards.
Process transactions securely with Braintreepayments.com.
Accept recurring and one-time payments.
Complete integration with Restrict Content Pro’s payment tracking system.
Users with recurring subscriptions can update their credit card info at any time.
Users with recurring subscriptions can cancel their subscription at any time, from your site.
Makes the short code available.