Add notify MFA module

source/_docs/authentication/multi-factor-auth.markdown

@@ -42,7 +42,7 @@ Below is a list of the currently available auth providers.
 
 [Time-based One-Time Password](https://en.wikipedia.org/wiki/Time-based_One-time_Password_algorithm) is widely adopted in modern authencation system, it combines a secret key with the current timestamp using a cryptographic hash function to generate a one-time password. Whoever possessed the secret key will get same one-time password in certain time period. By verifying that password, Home Assistant knows the user have the right secrt key.
 
-When trying to set up TOTP module, a QR code will show up. The user can scan it by an authenticator app, or set it up manually using the code showed in the UI. After setup, the user needs to input a six digit number generated in the autendicator app to verify the setup is good. If the verification keeps failing, you need to check whether the clock on Home Assistant is accurate.
+When trying to set up TOTP module, a QR code will show up. The user can scan it by an authenticator app, or set it up manually using the code showed in the UI. After setup, the user needs to input a six digit number generated in the authenticator app to verify the setup is good. If the verification keeps failing, you need to check whether the clock on Home Assistant is accurate.
 
 There are several authenticator apps on the market, we recommend either [Google Authenticator](https://support.google.com/accounts/answer/1066447) or [Authy](https://authy.com/).
 
@@ -52,10 +52,48 @@ Please treat the secret key like a password, never expose it to others.
 
 By default, one TOTP multi-factor named "Authenticator app" will be auto loaded if no `auth_mfa_modules` configuration section defined in the `configuration.yaml` file.
 
+By default one TOTP multi-factor auth module named "Authenticator app" will be auto loaded if no `auth_mfa_modules` config section defined in `configuration.yaml`.
+
 Example of configuration:
 
 ```yaml
 homeassistant:
   auth_mfa_modules:
     - type: totp
 ```
+
+### {% linkable_title Notify mutli-factor authentication module %}
+
+Notify MFA module using [notify component](https://www.home-assistant.io/components/notify/) to delivery a [HMAC-based One-Time Password](https://en.wikipedia.org/wiki/HMAC-based_One-time_Password_algorithm) to user configured target.
+
+User need first set up the MFA module by select one of the aviliable notify service. A 8 digit one-time password will be sent by this notify service, user need to input it to verify the setup.
+
+During the login process, an 8 digit one-time password will be sent again, user need to input it to verify his/her identity. If the validation failed, a new one-time password will be sent again.
+
+<p class='note'>
+Notify MFA module would not verify the one-time password deliveried success, so that if user cannot received the message due any reason, he/she may not be login again. Edit or remove `[your_config_dir]/.storage/auth_module.notify` can disable nofiy MFA module to resolve the issue.
+</p>
+
+Example of configuration
+
+```yaml
+homeassistant:
+  auth_mfa_modules:
+    - type: notify
+```
+
+Optional configuration variables:
+
+- **exclude** (*Optional*): The list of notify services you do not want to include in.
+- **include** (*Optional*): The list of notify services you want to include in.
+- **message** (*Optional*): The message template
+
+```yaml
+# Example configure with message template
+homeassistant:
+  auth_mfa_modules:
+    - type: totp
+      name: Authenticator app
+    - type: notify
+      message: 'I almost forget, to get into my clubhouse, you need to say {}'
+```