Flask-Security bootstraps your application with various views for handling its configured features to get you up and running as quickly as possible. However, you’ll probably want to change the way these views look to be more in line with your application’s visual design.


Flask-Security is packaged with a default template for each view it presents to a user. Templates are located within a subfolder named security. The following is a list of view templates:

  • security/forgot_password.html

  • security/login_user.html

  • security/mf_recovery.html

  • security/mf_recovery_codes.html

  • security/register_user.html

  • security/reset_password.html

  • security/change_password.html

  • security/send_confirmation.html

  • security/send_login.html

  • security/verify.html

  • security/two_factor_select.html

  • security/two_factor_setup.html

  • security/two_factor_verify_code.html

  • security/us_signin.html

  • security/us_setup.html

  • security/us_verify.html

  • security/wan_register.html

  • security/wan_signin.html

  • security/wan_verify.html

Overriding these templates is simple:

  1. Create a folder named security within your application’s templates folder

  2. Create a template with the same name for the template you wish to override

You can also specify custom template file paths in the configuration.

Each template is passed a template context object that includes the following, including the objects/values that are passed to the template by the main Flask application context processor:

  • <template_name>_form: A form object for the view.

  • security: The Flask-Security extension object.

  • url_for_security: A function that returns the configured URL for the passed Security endpoint.

  • _fsdomain: A function used to tag strings for extraction and localization.

  • _fs_is_user_authenticated: Returns True if argument (user) is authenticated. Usually the current_user proxy is the appropriate argument.

To add more values to the template context, you can specify a context processor for all views or a specific view. For example:

security = Security(app, user_datastore)

# This processor is added to all templates
def security_context_processor():
    return dict(hello="world")

# This processor is added to only the register view
def security_register_processor():
    return dict(something="else")

The following is a list of all the available context processor decorators:

  • context_processor: All views

  • forgot_password_context_processor: Forgot password view

  • login_context_processor: Login view

  • mf_recovery_codes_context_processor: Setup recovery codes view

  • mf_recovery_context_processor: Use recovery code view

  • register_context_processor: Register view

  • reset_password_context_processor: Reset password view

  • change_password_context_processor: Change password view

  • send_confirmation_context_processor: Send confirmation view

  • send_login_context_processor: Send login view

  • mail_context_processor: Whenever an email will be sent

  • tf_select_context_processor: Two factor select view

  • tf_setup_context_processor: Two factor setup view

  • tf_token_validation_context_processor: Two factor token validation view

  • us_signin_context_processor: Unified sign in view

  • us_setup_context_processor: Unified sign in setup view

  • wan_register_context_processor: WebAuthn registration view

  • wan_signin_context_processor: WebAuthn sign in view

  • wan_verify_context_processor: WebAuthn verify view


All forms can be overridden. For each form used, you can specify a replacement class. This allows you to add extra fields to any form or override validators. For example it is often desired to add additional personal information fields to the registration form:

from flask_security import RegisterForm
from wtforms import StringField
from wtforms.validators import DataRequired

class ExtendedRegisterForm(RegisterForm):
    first_name = StringField('First Name', [DataRequired()])
    last_name = StringField('Last Name', [DataRequired()])

security = Security(app, user_datastore,

For the register_form and confirm_register_form, only fields that exist in the user model are passed (as kwargs) to UserDatastore.create_user(). Thus, in the above case, the first_name and last_name fields will only be passed if the model looks like:

class User(db.Model, UserMixin):
    id = db.Column(db.Integer, primary_key=True)
    email = db.Column(db.String(255), unique=True)
    password = db.Column(db.String(255))
    first_name = db.Column(db.String(255))
    last_name = db.Column(db.String(255))


Adding fields is fine - however re-defining existing fields could cause various views to no longer function. Many fields have complex (and not publicly exposed) validators that have side effects.


It is important to ALWAYS subclass the base Flask-Security form and not attempt to just redefine the class. This is due to the validation method of many of the forms performs critical additional validation AND will change or add values to the form as a side-effect. See below for how to do this.

If you need to override an existing field in a form (to override/add validators), and you want to define a re-usable validator - use multiple inheritance - be extremely careful about the order of the inherited classes:

from wtforms import PasswordField, ValidationError
from wtforms.validators import DataRequired

def password_validator(form, field):
        raise ValidationError("Really - don't start a password with PASS")

class NewPasswordFormMixinEx:
    password = PasswordField("password",

class MyRegisterForm(NewPasswordFormMixinEx, ConfirmRegisterForm):

app.config["SECURITY_CONFIRM_REGISTER_FORM"] = MyRegisterForm

The following is a list of all the available form overrides:

  • login_form: Login form

  • verify_form: Verify form

  • confirm_register_form: Confirmable register form

  • register_form: Register form

  • forgot_password_form: Forgot password form

  • reset_password_form: Reset password form

  • change_password_form: Change password form

  • send_confirmation_form: Send confirmation form

  • mf_recovery_codes_form: Setup recovery codes form

  • mf_recovery_form: Use recovery code form

  • passwordless_login_form: Passwordless login form

  • two_factor_verify_code_form: Two-factor verify code form

  • two_factor_select_form: Two-factor select form

  • two_factor_setup_form: Two-factor setup form

  • two_factor_rescue_form: Two-factor help user form

  • us_signin_form: Unified sign in form

  • us_setup_form: Unified sign in setup form

  • us_setup_validate_form: Unified sign in setup validation form

  • us_verify_form: Unified sign in verify form

  • wan_delete_form: WebAuthn delete a registered key form

  • wan_register_form: WebAuthn initiate registration ceremony form

  • wan_register_response_form: WebAuthn registration ceremony form

  • wan_signin_form: WebAuthn initiate sign in ceremony form

  • wan_signin_response_form: WebAuthn sign in ceremony form

  • wan_verify_form: WebAuthn verify form


Changing/extending the form class won’t directly change how it is displayed. You need to ALSO provide your own template and explicitly add the new fields you want displayed.

Controlling Form Instantiation

This is an advanced concept! Please see Security.set_form_info() and FormInfo.

This is an example of providing your own form instantiator using the ‘form clone’ pattern. In this example we are injecting an external service into the form for use in validation:

from flask_security import FormInfo

class MyLoginForm(LoginForm):
    def __init__(self, *args, service=None, **kwargs):
        super().__init__(*args, **kwargs)
        self.myservice = service

    def instantiator(self, form_name, form_cls, *args, **kwargs):
        return MyLoginForm(*args, service=self.myservice, **kwargs)

    def validate(self, **kwargs: t.Any) -> bool:
        if not super().validate(**kwargs):  # pragma: no cover
            return False
        if not self.myservice(
  "Not happening")
            return False
        return True

# A silly service that only allows 'matt'' log in!
def login_checker(email):
    return True if email == "" else False

with app.test_request_context():
    # Flask-WTForms require a request context.
    fi = MyLoginForm(formdata=None, service=login_checker)"login_form", FormInfo(fi.instantiator))

Customizing the Login Form

This is an example of how to modify the registration and login form to add support for a single input field to accept both email and username (mimicking legacy Flask-Security behavior). Flask-Security supports username as a configuration option so this is not strictly needed any more, however, Flask-Security’s LoginForm uses 2 different input fields (so that appropriate input attributes can be set):

from flask_security import (
    from werkzeug.local import LocalProxy
    from wtforms import StringField, ValidationError, validators

    def username_validator(form, field):
        # Side-effect - is updated to normalized value.
        # Use proxy to we can declare this prior to initializing Security.
        _security = LocalProxy(lambda: app.extensions["security"])
        msg, = _security._username_util.validate(
        if msg:
            raise ValidationError(msg)

    class MyRegisterForm(RegisterForm):
        # Note that unique_identity_attribute uses the defined field 'mapper' to
        # normalize. We validate before that to give better error messages and
        # to set the normalized value into the form for saving.
        username = StringField(

    class MyLoginForm(LoginForm):
        email = StringField("email", [validators.data_required()])

        def validate(self, **kwargs):
            self.user = lookup_identity(
            # Setting 'ifield' informs the default login form validation
            # handler that the identity has already been confirmed.
            self.ifield =
            if not super().validate(**kwargs):
                return False
            return True

    # Allow registration with email, but login only with username
        {"username": {"mapper": uia_username_mapper}}
    security = Security(


All messages, form labels, and form strings are localizable. Flask-Security uses Flask-Babel to manage its messages.


Be sure to explicitly initialize your babel extension:

import flask_babel


All translations are tagged with a domain, as specified by the configuration variable SECURITY_I18N_DOMAIN (default: “flask_security”). For messages and labels all this works seamlessly. For strings inside templates it is necessary to explicitly ask for the “flask_security” domain, since your application itself might have its own domain. Flask-Security places the method _fsdomain in jinja2’s global environment and uses that in all templates. In order to reference a Flask-Security translation from ANY template (such as if you copied and modified an existing security template) just use that method:

{{ _fsdomain("Login") }}

Be aware that Flask-Security will validate and normalize email input using the email_validator package. The normalized form is stored in the DB.

Overriding Messages

It is possible to change one or more messages (either the original default english and/or a specific translation). Adding the following to your app:

app.config["SECURITY_MSG_INVALID_PASSWORD"] = ("Password no-worky", "error")

will change the default message in english.


The string messages themselves are a ‘key’ into the translation .po/.mo files. Do not pass in gettext(‘string’) or lazy_gettext(‘string).

If you need translations then you need to create your own translations directory and add the appropriate .po files and compile them. Finally, add your translations directory path to the configuration. In this example, create a file flask_security.po under a directory: translations/fr_FR/LC_MESSAGES (for french) with the following contents:

msgid ""
msgstr ""

msgid "Password no-worky"
msgstr "Passe - no-worky"

Then compile it with:

pybabel compile -d translations/ -i translations/fr_FR/LC_MESSAGES/flask_security.po -l fr_FR -D flask_security

Finally add your translations directory to your configuration:

app.config["SECURITY_I18N_DIRNAME"] = ["builtin", "translations"]


Flask-Security is also packaged with a default template for each email that it may send. Templates are located within the subfolder named security/email. The following is a list of email templates:

  • security/email/confirmation_instructions.html

  • security/email/confirmation_instructions.txt

  • security/email/login_instructions.html

  • security/email/login_instructions.txt

  • security/email/reset_instructions.html

  • security/email/reset_instructions.txt

  • security/email/reset_notice.html

  • security/email/reset_notice.txt

  • security/email/change_notice.txt

  • security/email/change_notice.html

  • security/email/welcome.html

  • security/email/welcome.txt

  • security/email/welcome_existing.html

  • security/email/welcome_existing.txt

  • security/email/welcome_existing_username.html

  • security/email/welcome_existing_username.txt

  • security/email/two_factor_instructions.html

  • security/email/two_factor_instructions.txt

  • security/email/two_factor_rescue.html

  • security/email/two_factor_rescue.txt

  • security/email/us_instructions.html

  • security/email/us_instructions.txt

Overriding these templates is simple:

  1. Create a folder named security within your application’s templates folder

  2. Create a folder named email within the security folder

  3. Create a template with the same name for the template you wish to override

Each template is passed a template context object that includes values as described below. In addition, the security object is always passed - you can for example render any security configuration variable via security.lower_case_variable_name and don’t include the prefix security_ (e.g. {{ security.confirm_url })}. If you require more values in the templates, you can specify an email context processor with the mail_context_processor decorator. For example:

security = Security(app, user_datastore)

# This processor is added to all emails
def security_mail_processor():
    return dict(hello="world")

There are many configuration variables associated with emails, and each template will receive a slightly different context. The Gate Config column are configuration variables that if set to False will bypass sending of the email (they all default to True). In most cases, in addition to an email being sent, a Signal is sent. The table below summarizes all this:

Template Name

Gate Config

Subject Config

Context Vars

Signal Sent




  • user

  • confirmation_link

  • confirmation_token





  • user

  • confirmation_link

  • confirmation_token





  • user

  • login_link

  • login_token





  • user

  • reset_link

  • reset_token





  • user





  • user





  • user

  • token

  • username





  • user





  • user

  • login_token

  • login_link

  • username





  • user

  • recovery_link





  • email

  • username


When sending an email, Flask-Security goes through the following steps:

  1. Calls the email context processor as described above

  2. Calls render_template (as configured at Flask-Security initialization time) with the context and template to produce a text and/or html version of the message

  3. Calls MailUtil.send_mail() with all the required parameters.

The default implementation of MailUtil.send_mail uses flask-mailman to create and send the message. By providing your own implementation, you can use any available python email handling package.

Email subjects are by default localized - see above section on Localization to learn how to customize them.

Emails with Celery

Sometimes it makes sense to send emails via a task queue, such as Celery. This is supported by providing your own implementation of the MailUtil class:

from flask_security import MailUtil
class MyMailUtil(MailUtil):

    def send_mail(self, template, subject, recipient, sender, body, html, **kwargs):

Then register your class as part of Flask-Security initialization:

from flask import Flask
from flask_mailman import EmailMultiAlternatives, Mail
from flask_security import Security, SQLAlchemyUserDatastore
from celery import Celery

mail = Mail()
security = Security()
celery = Celery()

def send_flask_mail(**kwargs):
    with app.app_context():
        with mail.get_connection() as connection:
            html = kwargs.pop("html", None)
            msg = EmailMultiAlternatives(**kwargs, connection=connection)
            if html:
                msg.attach_alternative(html, "text/html")

def create_app(config):
    """Initialize Flask instance."""

    app = Flask(__name__)

    datastore = SQLAlchemyUserDatastore(db, User, Role)
    security.init_app(app, datastore, mail_util_cls=MyMailUtil)

    return app


Flask-Security will likely be a very small piece of your application, so Flask-Security makes it easy to override all aspects of API responses.

JSON Response

Applications that support a JSON based API need to be able to have a uniform API response. Flask-Security has a default way to render its API responses - which can be easily overridden by providing a callback function via Security.render_json(). Be aware that Flask-Security subclasses Flask’s JSONProvider interface and sets it on app.json_provider_cls.

401, 403, Oh My

For a very long read and discussion; look at this. Out of the box, Flask-Security in tandem with Flask-Login, behaves as follows:

  • If authentication fails as the result of a @login_required, @auth_required(“session”, “token”), or @token_auth_required then if the request ‘wants’ a JSON response, Security.render_json() is called with a 401 status code. If not then the SECURITY_MSG_UNAUTHENTICATED message is flashed and the request is redirected to the login view.

  • If authentication fails as the result of a @http_auth_required or @auth_required(“basic”) then a 401 is returned along with the http header WWW-Authenticate set to Basic realm="xxxx". The realm name is defined by SECURITY_DEFAULT_HTTP_AUTH_REALM.

  • If authorization fails as the result of @roles_required, @roles_accepted, @permissions_required, or @permissions_accepted, then if the request ‘wants’ a JSON response, Security.render_json() is called with a 403 status code. If not, then if SECURITY_UNAUTHORIZED_VIEW is defined, the response will redirected. If SECURITY_UNAUTHORIZED_VIEW is not defined, then abort(403) is called.

All this can be easily changed by registering any or all of Security.render_json(), Security.unauthn_handler() and Security.unauthz_handler().

The decision on whether to return JSON is based on:

  • Was the request content-type “application/json” (e.g. request.is_json()) OR

  • Is the ‘best’ value of the Accept HTTP header “application/json”


Flask-Security uses redirects frequently (when using forms), and most of the redirect destinations are configurable. When Flask-Security initiates a redirect it (almost) always flashes a message that provides some context for the user. In addition, Flask-Security - both in its views and default templates, attempts to propagate any next query param and in fact, an existing ?next=/xx will override most of the configuration redirect URLs.

As a complex example consider an unauthenticated user accessing a @auth_required endpoint, and the user has two-factor authentication set up.:

  • GET(“/protected”) - The default_unauthn_handler will redirect to /login?next=/protected

  • The login form/template will pick any ?next=/xx argument off the request URL and append it to form action.

  • When the form is submitted if will do a POST(“/login?next=/protected”)

  • Assuming correct authentication, the system will send out a 2-factor code and redirect to /tf-verify?next=/protected

  • The two_factor_validation_form/template also pulls any ?next=/xx and appends to the form action.

  • When the tf-validate form is submitted it will do a POST(“/tf-validate?next=/protected”).

  • Assuming a correct code, the user is authenticated and is redirected. That redirection first looks for a ‘next’ in the request.args then in request.form and finally will use the value of SECURITY_POST_LOGIN_VIEW. In this example it will find the next=/protected in the request.args and redirect to /protected.