developers.home-assistant/docs/auth_auth_module.md

title
Multi-factor authentication modules

Multi-factor Authentication Modules are used in conjunction with Authentication Provider to provide a fully configurable authentication framework. Each MFA module may provide one multi-factor authentication function. User can enable multiple mfa modules, but can only select one module in login process.

Defining an mfa auth module

:::info We currently only support built-in mfa auth modules. Support for custom auth modules might arrive in the future. :::

Multi-factor Auth modules are defined in homeassistant/auth/mfa_modules/<name of module>.py. The auth module will need to provide an implementation of the MultiFactorAuthModule class.

For an example of a fully implemented auth module, please see insecure_example.py.

Multi-factor Auth modules shall extend the following methods of MultiFactorAuthModule class.

method	Required	Description
@property def input_schema(self)	Yes	Return a schema defined the user input form.
async def async_setup_flow(self, user_id)	Yes	Return a SetupFlow to handle the setup workflow.
async def async_setup_user(self, user_id, setup_data)	Yes	Set up user for use this auth module.
async def async_depose_user(self, user_id)	Yes	Remove user information from this auth module.
async def async_is_user_setup(self, user_id)	Yes	Return whether user is set up.
async def async_validate(self, user_id, user_input)	Yes	Given a user_id and user input, return validation result.
async def async_initialize_login_mfa_step(self, user_id)	No	Will be called once before display the mfa step of login flow. This is not initialization for the MFA module but the mfa step in login flow.

Setup flow

Before user can use a multi-factor auth module, it has to be enabled or set up. All available modules will be listed in user profile page, user can enable the module he/she wants to use. A setup data entry flow will guide user finish the necessary steps.

Each MFA module need to implement a setup flow handler extends from mfa_modules.SetupFlow (if only one simple setup step need, SetupFlow can be used as well). For example for Google Authenticator (TOTP, Time-based One Time Password) module, the flow will need to be:

• Generate a secret and store it on instance of setup flow
• Return async_show_form with a QR code in the description (injected as base64 via description_placeholders)
• User scans code and enters a code to verify it scanned correctly and clock in synced
• TOTP module saved the secret along with user_id, module is enabled for user

Workflow

Configuration example

# configuration.xml
homeassistant:
  auth_providers:
    - type: homeassistant
    - type: legacy_api_password
  auth_mfa_modules:
    - type: totp
    - type: insecure_example
      users: [{'user_id': 'a_32_bytes_length_user_id', 'pin': '123456'}]

In this example, user will first select from homeassistant or legacy_api_password auth provider. For homeassistant auth provider, user will first input username/password, if that user enabled both totp and insecure_example, then user need select one auth module, then input Google Authenticator code or input pin code base on the selection.

:::tip insecure_example is only for demo purpose, please do not use it in production. :::

Validation session

Not like auth provider, auth module use session to manage the validation. After auth provider validated, mfa module will create a validation session, include an expiration time and user_id from auth provider validate result. Multi-factor auth module will not only verify the user input, but also verify the session is not expired. The validation session data is stored in your configuration directory.