user7197914 user7197914 - 17 days ago 13
Python Question

TypeError: Expecting a string- or bytes-formatted key when using Flask-JWT

I have a question about flask python.
I tried learning how to build a web using flask, and there is some error. In this case I am using mongoengine as database and JWT(Json Web Token) and the alert error is like this: "TypeError: Expecting a string- or bytes-formatted key"

192.168.100.26 - - [22/Nov/2016 22:50:08] "POST /auth HTTP/1.1" 500 -
Traceback (most recent call last):
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 2000, in __call__
return self.wsgi_app(environ, start_response)
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 1991, in wsgi_app
response = self.make_response(self.handle_exception(e))
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 1567, in handle_exception
reraise(exc_type, exc_value, tb)
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 1988, in wsgi_app
response = self.full_dispatch_request()
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 1641, in full_dispatch_request
rv = self.handle_user_exception(e)
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 1544, in handle_user_exception
reraise(exc_type, exc_value, tb)
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 1639, in full_dispatch_request
rv = self.dispatch_request()
File "/home/def/.local/lib/python2.7/site-packages/flask/app.py", line 1625, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)
File "/home/def/pr/flask/flask_deeper/test/routes/auth.py", line 26, in auth
access_token = _jwt.jwt_encode_callback(identity)
File "/usr/local/lib/python2.7/dist-packages/flask_jwt/__init__.py", line 70, in _default_jwt_encode_handler
return jwt.encode(payload, secret, algorithm=algorithm, headers=headers)
File "/usr/local/lib/python2.7/dist-packages/jwt/api_jwt.py", line 56, in encode
json_payload, key, algorithm, headers, json_encoder
File "/usr/local/lib/python2.7/dist-packages/jwt/api_jws.py", line 98, in encode
key = alg_obj.prepare_key(key)
File "/usr/local/lib/python2.7/dist-packages/jwt/algorithms.py", line 116, in prepare_key
raise TypeError('Expecting a string- or bytes-formatted key.')
TypeError: Expecting a string- or bytes-formatted key.


I thought the error was at this.

models/user.py

@staticmethod
def jwt_handler(token):
if not User.objects(token=token):
raise JWTError("Bad bad bad bad")

secret = str(current_app.config["JWT_SECRET_KEY"])
algorithm = str(current_app.config["JWT_ALGORITHM"])
options = {
'verify_' + claim: True
for claim in verify_claims
}

options.update({
'require_' + claim: True
for claim in required_claims
})

decode = jwt.decode(token, secret, options=options, algorithms=[algorithm])
return decode

@staticmethod
def authenticate(username, password):
user = User.objects(username=username)
if len(user) == 0:
return None
user = user[0]
user["id"] = str(user["id"])

if crypt.verify(password, user.password):
return user

return user


routes/user.py

def auth():
username = request.form.get("username")
password = request.form.get("password")

if not username:
raise BadRequest("Userna doesn't exists")

user = user_ctrl.read(username)

identity = _jwt.authentication_callback(username, password)

if identity:
access_token = _jwt.jwt_encode_callback(identity)
identity.update(push__token=access.decode("utf8"))
return _jwt.auth_response_callback(access_token, identity)
else:
raise JWTError("Bad bad bad very bad")


config.py

import os
from test.models import db

class Config(object):

db_name = os.getenv('MONGODB_NAME', 'third')
db_host = os.getenv('MONGODB_HOST', '127.0.0.1')
db_port = os.getenv('MONGODB_PORT', '5000')

JWT_SECRET_KEY = 'test123'
JWT_ALGORITHM = 'SH256'
JWT_AUTH_ENDPOINT = 'jwt'
JWT_AUTH_USERNAME_KEY = 'username'
JWT_AUTH_PASSWORD_KEY = 'password'


http.py

import logging.config
import jwt
from flask_jwt import JWT
from flask import Flask

from test import routes
from test.models import db, User

_jwt = JWT(authentication_handler=User.authenticate, identity_handler=User.identity)
_jwt.jwt_decode_callback=User.jwt_handler

def create_app(config):
app = Flask(__name__.split(',')[0])

app.register_blueprint(routes.user.bp)
app.register_blueprint(routes.auth.bp)

db.init_app(app)

_jwt.init_app(app)

return app

Answer

You have defined the configuration is config.py but have not added the configuration object to your flask app. Therefore, keys such as JWT_SECRET_KEY are not in your app config.

Flask-JWT's default_handler expects those values (Copied in case source changes)

def _default_jwt_decode_handler(token):
    secret = current_app.config['JWT_SECRET_KEY']
    algorithm = current_app.config['JWT_ALGORITHM']
    leeway = current_app.config['JWT_LEEWAY']

In your case as that is not set, it returns None and trips the algorithms.py (which expects a string key).

Therefore, during your app initialization in http.py, you must add a call to app.config.from_object. Maybe something like this

def create_app(config):
    app = Flask(__name__.split(',')[0])

    # Edit the following to point it to your Config class
    app.config.from_object(config.Config)

    app.register_blueprint(routes.user.bp)
    app.register_blueprint(routes.auth.bp)

    db.init_app(app)

    _jwt.init_app(app)

    return app

On a side note, the name of JWT_ALGORITHM should be HS256 rather than SH256 (Although it doesn't matter as HS256 is the default and will be chosen since SH256 is not a valid algorithm)