.. _authentication_modes: .. _client_modes: Authentication Modes and Client Modes ===================================== eduMFA supports a variety of tokens that implement different authentication flows. We call these flows *authentication modes*. Currently, tokens may implement three authentication modes, namely ``authenticate``, ``challenge`` and ``outofband``. Application plugins need to implement the three authentication modes separately, as the modes differ in their user experience. To help the plugins identify the flow, the JSON response of an authentication request contains additional information in the section .. code-block:: json { "detail": "multi_challenge": [ { "client_mode": "poll", } ] } The "client_mode" gives the plugin even more information how to respond. The authentication mode ``challenge`` can either result in client_mode ``interactive``, ``webauthn`` of ``u2f`` and the authentication mode ``outofband`` can currently result in client mode ``poll``. Here are examples for the flows: * The HOTP token type implements the ``authenticate`` mode, which is a single-shot authentication flow. For each authentication request, the user uses their token to generate a new HOTP value and enters it along with their OTP PIN. The plugin sends both values to eduMFA, which decides whether the authentication is valid or not. * The E-Mail and SMS token types implement the ``challenge`` mode. With such a token, the authentication flow consists of two steps: In a first step, the plugin triggers a challenge. eduMFA sends the challenge response --- a fresh OTP value --- to the user via E-Mail or SMS. In a second step, the user responds to the challenge by entering the respective OTP value in the plugin's login form. The plugin sends the challenge response to eduMFA, which decides whether the authentication is valid or not. The "client_mode" is set to ``interactive``. This indicates that the plugin should display an input field, so that the user can enter the response interactively. * WebAuthn tokens and U2F tokens also implement the ``challenge`` mode. However, the plugin needs to handle these challenges differently, since the user does not need to enter the response to the challenge manually. The "client_mode" is either set to ``webauthn`` or ``u2f`` so that the plugin can handle the cryptographic challenge accordingly. * The PUSH and TiQR token types implement the ``outofband`` mode. With PUSH tokens, the authentication step also consists of two steps: In a first step, the user triggers a challenge. eduMFA pushes the challenge to the user's smartphone app. In a second step, the user approves the challenge on their phone, and the app responds to the challenge by communicating with the eduMFA server on behalf of the user. The plugin periodically queries eduMFA to check if the challenge has been answered correctly and the authentication is valid. In this case the "client_mode" is set to ``poll``, so that the plugin knows, that it needs to poll for the response to the challenge. The following describes the authentication flows of the three authentication modes in more detail. .. _authentication_mode_authenticate: ``authenticate`` mode --------------------- .. figure:: images/auth_mode_authenticate.png :width: 250 The *Service* is an application that is protected with a second factor by eduMFA. * The user enters a OTP PIN along with an OTP value at the *Service*. * The plugin sends a request to the ``/validate/check`` endpoint of eduMFA: .. code-block:: text POST /validate/check user=&pass= and eduMFA returns whether the authentication request has succeeded or not. .. _authentication_mode_challenge: ``challenge`` mode ------------------ .. figure:: images/auth_mode_challenge.png :width: 450 * The plugin triggers a challenge, for example via the ``/validate/triggerchallenge`` endpoint: .. code-block:: text POST /validate/triggerchallenge user= Alternatively, a challenge can be triggered via the ``/validate/check`` endpoint with the PIN of a challenge-response token: .. code-block:: text POST /validate/check user=&pass= In both variants, the plugin receives a transaction ID which we call ``transaction_id`` and asks the user for the challenge response. * The user enters the challenge response, which we call ``OTP``. The plugin forwards the response to eduMFA along with the transaction ID: .. code-block:: text POST /validate/check user=&transaction_id=&pass= and eduMFA returns whether the authentication request succeeded or not. .. _authentication_mode_outofband: ``outofband`` mode ------------------ .. figure:: images/auth_mode_outofband.png :width: 550 * The plugin triggers a challenge, for example via the ``/validate/triggerchallenge`` endpoint: .. code-block:: text POST /validate/triggerchallenge user= or via the ``/validate/check`` endpoint with the PIN of a out-of-band token: .. code-block:: text POST /validate/check user=&pass= In both variants, the plugin receives a transaction ID which we call ``transaction_id``. The plugin may now periodically query the status of the challenge by polling the ``/validate/polltransaction`` endpoint: .. code-block:: text GET /validate/polltransaction transaction_id= If this endpoint returns ``false``, the challenge has not been answered yet. * The user approves the challenge on a separate device, e.g. their smartphone app. The app communicates with a tokentype-specific endpoint of eduMFA, which marks the challenge as answered. The exact communication depends on the token type. * Once ``/validate/polltransaction`` returns ``true``, the plugin *must* finalize the authentication via the ``/validate/check`` endpoint: .. code-block:: text POST /validate/check user=&transaction_id=&pass= For the ``pass`` parameter, the plugin sends an empty string. This step is crucial because the ``/validate/check`` endpoint takes defined authentication and authorization policies into account to decide whether the authentication was successful or not. .. note:: The ``/validate/polltransaction`` endpoint does not require authentication and does not increase the failcounters of tokens. Hence, attackers may try to brute-force transaction IDs of correctly answered challenges. Due to the short expiration timeout and the length of the randomly-generated transaction IDs, it is unlikely that attackers correctly guess a transaction ID in time. Nonetheless, plugins must not allow users to inject transaction IDs, and plugins must not leak transaction IDs to users.