Features

Flask-Security allows you to quickly add common security mechanisms to your Flask application. They include:

Session Based Authentication

Session based authentication is fulfilled entirely by the Flask-Login extension. Flask-Security handles the configuration of Flask-Login automatically based on a few of its own configuration values and uses Flask-Login’s alternative token feature to associate the value of fs_uniquifier with the user. (This enables easily invalidating all existing sessions for a given user without having to change their user id). Flask-WTF integrates with the session as well to provide out of the box CSRF support. Flask-Security extends that to support configurations that would require CSRF for requests that are authenticated via session cookies, but not for requests authenticated using tokens.

Role/Identity Based Access

Flask-Security implements very basic role management out of the box. This means that you can associate a high level role or multiple roles to any user. For instance, you may assign roles such as Admin, Editor, SuperUser, or a combination of said roles to a user. Access control is based on the role name and/or permissions contained within the role; and all roles should be uniquely named. This feature is implemented using the Flask-Principal extension. As with basic RBAC, permissions can be assigned to roles to provide more granular access control. Permissions can be associated with one or more roles (the RoleModel contains a list of permissions). The values of permissions are completely up to the developer - Flask-Security simply treats them as strings. If you’d like to implement even more granular access control (such as per-object), you can refer to the Flask-Principal documentation on this topic.

Password Hashing

Password hashing is enabled with passlib. Passwords are hashed with the bcrypt function by default but you can easily configure the hashing algorithm. You should always use a hashing algorithm in your production environment. Hash algorithms not listed in SECURITY_PASSWORD_SINGLE_HASH will be double hashed - first an HMAC will be computed, then the selected hash function will be used. In this case - you must provide a SECURITY_PASSWORD_SALT. A good way to generate this is:

secrets.SystemRandom().getrandbits(128)

Bear in mind passlib does not assume which algorithm you will choose and may require additional libraries to be installed.

Password Validation and Complexity

Consult Password Validation and Complexity.

Basic HTTP Authentication

Basic HTTP authentication is achievable using a simple view method decorator. This feature expects the incoming authentication information to identify a user in the system. This means that the username must be equal to their email address.

Token Authentication

Token based authentication can be used by retrieving the user auth token from an authentication endpoint (e.g. /login, /us-signin). Perform an HTTP POST with a query param of include_auth_token and the authentication details as JSON data. A successful call will return the authentication token. This token can be used in subsequent requests to protected resources. The auth token should be supplied in the request through an HTTP header or query string parameter. By default the HTTP header name is Authentication-Token and the default query string parameter name is auth_token.

Authentication tokens are generated using a uniquifier field in the user’s UserModel. By default that field is fs_uniquifier. This means that if that field is changed (via UserDatastore.set_uniquifier()) then any existing authentication tokens will no longer be valid. This value is changed whenever a user changes their password. If this is not the desired behavior then you can add an additional attribute to the UserModel: fs_token_uniquifier and that will be used instead, thus isolating password changes from authentication tokens. That attribute can be changed via UserDatastore.set_token_uniquifier(). This attribute should have unique=True. Unlike fs_uniquifier, it can be set to nullable - it will automatically be generated at first use if null.

Two-factor Authentication

This feature is in Beta - mostly due to it being brand new and little to no production soak time

Two-factor authentication is enabled by generating time-based one time passwords (Tokens). The tokens are generated using the users totp secret, which is unique per user, and is generated both on first login, and when changing the two-factor method (doing this causes the previous totp secret to become invalid). The token is provided by one of 3 methods - email, sms (service is not provided), or an authenticator app such as Google Authenticator, LastPass Authenticator, or Authy. By default, tokens provided by the authenticator app are valid for 2 minutes, tokens sent by mail for up to 5 minute and tokens sent by sms for up to 2 minutes. The QR code used to supply the authenticator app with the secret is generated using the PyQRCode library. Please read Theory of Operation for more details.

Unified Sign In

This feature is in Beta - mostly due to it being brand new and little to no production soak time

Unified sign in provides a generalized login endpoint that takes an identity and a passcode; where (based on configuration):

  • identity is any of SECURITY_USER_IDENTITY_ATTRIBUTES (e.g. email, username, phone)

  • passcode is a password or a one-time code (delivered via email, SMS, or authenticator app)

Please see this Wikipedia article about multi-factor authentication.

Using this feature, it is possible to not require the user to have a stored password at all, and just require the use of a one-time code. The mechanisms for generating and delivering the one-time code are similar to common two-factor mechanisms.

This one-time code can be configured to be delivered via email, SMS or authenticator app - however be aware that NIST does not recommend email for this purpose (though many web sites do so) due to the fact that a) email may travel through many different servers as part of being delivered - and b) is available from any device.

Using SMS or an authenticator app means you are providing “something you have” (the mobile device) and either “something you know” (passcode to unlock your device) or “something you are” (biometric quality to unlock your device). This effectively means that using a one-time code to sign in, is in fact already two-factor (if using SMS or authenticator app). Many large authentication providers already offer this - here is Microsoft’s version.

Note that by configuring SECURITY_US_ENABLED_METHODS an application can use this endpoint JUST with identity/password or in fact disallow passwords altogether.

Unified sign in is integrated with two-factor authentication. Since in general there is no need for a second factor if the initial authentication was with SMS or an authenticator application, the SECURITY_US_MFA_REQUIRED configuration determines which primary authentication mechanisms require a second factor. By default limited to email and password (if two-factor is enabled).

Be aware that by default, the SECURITY_US_SETUP_URL endpoint is protected with a freshness check (see flask_security.auth_required()) which means it requires a session cookie to function properly. This is true even if using JSON payload or token authentication. If you disable the freshness check then sessions aren’t required.

Current Limited Functionality:

  • Change password does not work if a user registers without a password. However forgot-password will allow the user to set a new password.

  • Registration and Confirmation only work with email - so while you can enable multiple authentication methods, you still have to register with email.

Email Confirmation

If desired you can require that new users confirm their email address. Flask-Security will send an email message to any new users with a confirmation link. Upon navigating to the confirmation link, the user will be automatically logged in. There is also view for resending a confirmation link to a given email if the user happens to try to use an expired token or has lost the previous email. Confirmation links can be configured to expire after a specified amount of time.

Password Reset/Recovery

Password reset and recovery is available for when a user forgets their password. Flask-Security sends an email to the user with a link to a view which allows them to reset their password. Once the password is reset they are automatically logged in and can use the new password from then on. Password reset links can be configured to expire after a specified amount of time.

As with password change - this will update the the user’s fs_uniquifier attribute which will invalidate all existing sessions AND (by default) all authentication tokens.

User Registration

Flask-Security comes packaged with a basic user registration view. This view is very simple and new users need only supply an email address and their password. This view can be overridden if your registration process requires more fields. User email is validated and normalized using the email_validator package.

The SECURITY_USERNAME_ENABLE configuration option, when set to True, will add support for the user to register a username in addition to an email. By default, the user will be able to authenticate with EITHER email or username - however that can be changed via the SECURITY_USER_IDENTITY_ATTRIBUTES.

Password Change

Flask-Security comes packaged with a basic change user password view. Unlike password recovery, this endpoint is used when the user is already authenticated. The result of a successful password change is not only a new password, but a new value for fs_uniquifier. This has the effect is immediately invalidating all existing sessions. The change request itself effectively re-logs in the user so a new session is created. Note that since the user is effectively re-logged in, the same signals are sent as when the user normally authenticates.

NOTE: The fs_uniquifier by default, controls both sessions and authenticated tokens. Thus changing the password also invalidates all authentication tokens. This may not be desirable behavior, so if the UserModel contains an attribute fs_token_uniquifier, then that will be used when generating authentication tokens and so won’t be affected by password changes.

Login Tracking

Flask-Security can, if configured, keep track of basic login events and statistics. They include:

  • Last login date

  • Current login date

  • Last login IP address

  • Current login IP address

  • Total login count

JSON/Ajax Support

Flask-Security supports JSON/Ajax requests where appropriate. Please look at CSRF for details on how to work with JSON and Single Page Applications. More specifically JSON is supported for the following operations:

  • Login requests

  • Unified sign in requests

  • Registration requests

  • Change password requests

  • Confirmation requests

  • Forgot password requests

  • Passwordless login requests

  • Two-factor login requests

  • Change two-factor method requests

In addition, Single-Page-Applications (like those built with Vue, Angular, and React) are supported via customizable redirect links.

Command Line Interface

Basic Click commands for managing users and roles are automatically registered. They can be completely disabled or their names can be changed. Run flask --help and look for users and roles.