FlaskSimpleAuth 0.9.0

Simple authentication for Flask, emphasizing configurability

Flask Simple Auth

Simple authentication for Flask, which is controled from Flask configuration.

Description

Help to manage authentication (not autorizations) in a Flask application.

The idea is that the authentication is checked in a before_request hook, and can be made available through some global à-la-Flask variable.

The module implements inheriting the web-server authentication, password authentication (HTTP Basic, or HTTP/JSON parameters), simple time-limited authentication tokens, and a fake authentication mode useful for application testing.

It allows to have a login route to generate authentication tokens. Support functions allow to hash new passwords consistently with password checks.

Compared to Flask HTTPAuth, there is one code in the app which does not need to know about which mode is being used, so switching between modes only impacts the configuration, not the application code.

Example

The application code extract below maintains a LOGIN global variable which holds the authenticated user name for the current request.

There is no clue in the source about what kind of authentication is used, which is the whole point: authentication methods are managed elsewhere.

# app is a Flask application…

# initialize module
import FlaskSimpleAuth as auth
auth.setConfig(app, user_to_password_function)

# mandatory authentication
# note: some routes may need to skip this, eg for registering new users.
LOGIN = None

def set_login():
    global LOGIN
    LOGIN = None                  # remove previous value, just in case
    try:
        LOGIN = auth.get_user()    
    except auth.AuthException as e:
        return Response(e.message, e.status)
    assert LOGIN is not None      # defensive check

app.before_request(set_login)

# token creation route
@app.route("/login", methods=["GET"])
def get_login():
    return jsonify(auth.create_token(LOGIN)), 200

# elsewhere
@app.route("/whatever", methods=["POST"])
def post_whatever():
    # check authorization
    if not can_post_whatever(LOGIN):
        return "", 403
    # ok to do it
    return "", 201

Authentication is manage from the application flask configuration with FSA_* (Flask simple authentication) directives:

FSA_TYPE = 'httpd'     # inherit web-serveur authentication
# OR others such as:
FSA_TYPE = 'basic'     # HTTP Basic auth

Various aspects of the implemented schemes can be configured with other directives, with reasonable defaults provided so that not much is really needed beyond choosing the authentication scheme. See below for details.

Documentation

This simplistic module allows configurable authentication (FSA_TYPE):

• httpd web-server checked authentication passed in the request.

• fake parameter-based auth for fast and simple testing the claimed login is coldly trusted…

• basic http basic auth with a function hook for getting the password hash. Beware that modern password checking is often pretty expensive, so that you do not want to have to use that on every request in real life (eg 400 ms for passlib bcrypt 12 rounds, although 2 ms for 4 rounds is manageable).

• param same with http parameter-provided login/password.

• token auth uses a signed parameter to authenticate a user in a realm for some limited time. The token can be obtained by actually authenticating with previous methods.

I have considered flask_httpauth obviously, which provides many options, but I do not want to force their per-route model and explicit classes but rather rely on mandatory request hooks and have everything managed from the configuration file to easily switch between schemes.

Note that this is intended for a REST API implementation serving a remote application. It does not make much sense to "login" and "logout" to/from a REST API because the point of the API is to serve and collect data to all who deserve it, i.e. are authorized, unlike a web application which is served while the client is on the page and should disappear when disconnected as the web browser page is wiped out. However, there is still a "login" concept which is only dedicated at obtaining an auth token.

httpd Authentication

Inherit web server supplied authentication through request.remote_user. This is the default.

basic Authentication

HTTP Basic password authentication.

See also Password Authentication below for how the password is retrieved.

param Authentication

HTTP parameter or JSON password authentication.

The following configuration directives are available:

• FSA_PARAM_USER parameter name for the user name. Default is USER.
• FSA_PARAM_PASS parameter name for the password. Default is PASS.

See also Password Authentication below for how the password is retrieved.

token Authentication

Only rely on signed tokens for authentication. A token certifies that a user is authenticated up to some time limit. The token syntax is: <realm>:<user>:<limit>:<signature>

The following configuration directives are available:

• FSA_TOKEN_REALM realm of token. Default is the simplified lower case application name.
• FKA_TOKEN_NAME name of parameter holding the auth token. Default is auth.
• FSA_TOKEN_SECRET secret string used for signing tokens. Default is a system-generated random string containing 128 bits. This default with only work with itself.
• FSA_TOKEN_DELAY number of minutes a token validity. Default is 60 minutes.
• FSA_TOKEN_HASH hash algorithm used to sign the token. Default is blake2s.
• FSA_TOKEN_LENGTH number of hash bytes kept for token signature. Default is 32.

Function create_token(user) creates a token for the user.

fake Authentication

Trust a parameter for authentication claims. Only for local tests.

The following configuration directive is available:

• FSA_FAKE_LOGIN name of parameter holding the user name. Default is LOGIN.

Password Authentication (param or basic)

For checking passwords the password (hash) must be retrieved through get_user_password(user). This function must be provided by the application.

The following configuration directives are available to configure passlib password checks:

• FSA_PASSWORD_SCHEME password scheme to use for passwords. Default is bcrypt.
• FSA_PASSWORD_OPTIONS relevant options (for passlib.CryptContext). Default is {'bcrypt__default_rounds': 4}.

These defaults result in a manageable password checks of a few milliseconds.

Function hash_password(pass) computes the password salted digest compatible with the configuration.

Versions

Sources are available on GitHub.

No initial release yet.

TODO

Features

• implement 'password' which does anything with a password?
• test 'param'?

Implementation

• should it be an object instead of a flat module?

How not to forget autorizations?

• set a autorization_checked variable to False before the request
• reset it to True when autorization is checked
• check whether it was done and possibly abort after the request