What is the best practice for changing headers in a Flask request?

Question

I have a Flask app that uses a custom decorator to verify an AWS Cognito login token passed in an HTTP header attribute. The process includes refreshing the token (which is beyond the scope of this question). Once I get the refreshed token, I would like to update the header attribute to include the refreshed token and exit. Since the Flask/Werkzeug request.headers property is immutable, I can't update it by normal means.

How can I update the headers in the context of this decorator? Is there a better way that I am not thinking of?

Here's some sample code that demonstrates the issue:

def login_required(f):
    @wraps(f)
    def decorated_function(*args, **kwargs):
        token = request.headers.get('X-MyApp-Auth')
        if not token:
            return redirect(url_for('login', next=request.url))
        # Test for expired token (pseudocode)
        if expired(token):
            # Refresh the token (pseudocode)
            new_token = refresh(refresh_token)
            # This is the part where the immutability gets me stuck
            request.headers.set('X-MyApp-Auth', new_token)
        return f(*args, **kwargs)
    return decorated_function

Answer 1

This example wraps the Flask application in a custom WSGI middleware that modifies the WSGI environment before Flask request handling:

from flask import Flask, request, jsonify


class InterceptRequestMiddleware:
    def __init__(self, wsgi_app):
        self.wsgi_app = wsgi_app

    def __call__(self, environ, start_response):
        environ['HTTP_USER_AGENT'] = 'foobar'
        return self.wsgi_app(environ, start_response)


app = Flask(__name__)
app.wsgi_app = InterceptRequestMiddleware(app.wsgi_app)


@app.route('/')
def index():
    return jsonify({'headers': {k: v for k, v in request.headers}})


if __name__ == '__main__':
    app.run(debug=True)

Links:

• Flask.wsgi_app documentation
• http://ivory.idyll.org/articles/wsgi-intro/what-is-wsgi.html