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Flask is a lightweight WSGI web application framework in Python. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. Flask is known for its simplicity and flexibility, making it a popular choice for developers who want to build web applications with minimal overhead.
When working with Flask, you might encounter a common issue where a CSRF (Cross-Site Request Forgery) token is missing or incorrect. This typically manifests as an error message indicating that the CSRF token is either not present or does not match the expected value. This can prevent forms from being submitted successfully, leading to user frustration and potential security vulnerabilities.
CSRF tokens are a security measure used to protect web applications from cross-site request forgery attacks. These tokens are unique to each session and are required to be included in forms that modify data on the server. When a CSRF token is missing or incorrect, it means that the form submission is not properly authenticated, which can be due to several reasons such as missing token in the form, incorrect token handling, or session issues.
To resolve the CSRF token issue, follow these steps:
Make sure that every form in your application includes a CSRF token. In Flask, you can use the Flask-WTF
extension to handle CSRF protection easily. Here’s how you can include a CSRF token in your forms:
from flask_wtf import FlaskForm
from wtforms import StringField, SubmitField
from wtforms.validators import DataRequired
class MyForm(FlaskForm):
name = StringField('Name', validators=[DataRequired()])
submit = SubmitField('Submit')
In your HTML template, ensure you include {{ form.hidden_tag() }}
to render the CSRF token:
<form method="post">
{{ form.hidden_tag() }}
{{ form.name.label }}
{{ form.name() }}
{{ form.submit() }}
</form>
Ensure that your server-side logic correctly validates the CSRF token. Flask-WTF automatically checks the CSRF token when you use FlaskForm, but if you are handling tokens manually, make sure to compare the token from the form with the one stored in the session.
CSRF tokens are often stored in the session. Ensure that your session management is correctly configured and that the session is not being reset or lost between requests. You can configure session management in Flask using the SECRET_KEY
configuration:
app.config['SECRET_KEY'] = 'your_secret_key_here'
For more information on CSRF protection in Flask, you can refer to the following resources:
(Perfect for DevOps & SREs)
(Perfect for DevOps & SREs)